The sole assignment of error properly preserved for our consideration on this appeal is the failure of the trial court to instruct the jury on the doctrine of last clear chance. In its decision, the Court of Appeals concluded that last clear chance did not apply unless both parties were found negligent and held that the jury’s verdict in the instant case finding the operator of the truck not to be negligent mooted any possible error by the trial court in denying the requested instruction. We have determined that this holding was error; therefore, the decision of the Court of Appeals must be reversed.
When charging the jury in a civil case it is the duty of the trial court to explain the law and to apply it to the evidence on the substantial issues of the action. G.S. 1A-1, Rule 51; Superior Foods, Inc. v. Harris-Teeter Super Markets, Inc., 288 N.C. 213, 217 S.E. 2d 566 (1975); Investment Properties of Asheville, Inc. v. Norburn, 281 N.C. 191, 188 S.E. 2d 342 (1972). If a party contends that certain acts or omissions constitute a claim for relief or a defense against another, the trial court must submit the issue with appropriate instructions if there is evidence which, when viewed in the light most favorable to the proponent, will support a reasonable inference of each essential element of the claim or defense asserted. See, Vernon v. Crist, 291 N.C. 646, 231 S.E. 2d 591 (1977); Atkins v. Moye, 277 N.C. 179, 176 S.E. 2d 789 (1970).
The doctrine of last clear chance, if properly raised, should be submitted to the jury when the evidence tends to show “that after the plaintiff had, by his own negligence, gotten into a position of helpless peril (or into a position of peril to which he was inadvertent), the defendant discovered the plaintiff’s helpless peril (or inadvertence), or, being under a duty to do so, should have, and thereafter, the defendant having the means and the time to avoid the injury, negligently failed to do so.” Exum v. *450 Boyles, 272 N.C. 567, 576, 158 S.E. 2d 845, 853 (1968); accord, Vernon v. Crist, supra.
 Applying these principles to the record of the case sub judice, we hold that the trial court erred in denying plaintiff’s request for an instruction on the doctrine of last clear chance. The evidence, when viewed in the light most favorable to plaintiff, shows that the accident occurred at midday, when the highway was dry and free of defects and neither lane was burdened by other traffic. Moreover, the southbound traffic lane in the vicinity of the collision was approximately 12 feet wide, as was the west shoulder of the road; the westernmost gouge mark in the pavement, indicating the site of the left front portion of the Volkswagen at impact, was 6 feet 8 inches from the center line of the highway; and the truck was 8 feet wide. Although the shoulder of the road sloped off into a culvert running under the south driveway of the Institute, there were no obstructions on the shoulder south of the driveway which would have prevented a vehicle from parking there. In addition, the defendant truck driver told a highway patrolman investigating the accident that he “may have been running a little over the speed limit” at the time of the collision.
The defendant truck driver, in operating a motor vehicle upon the highway, was under a duty to keep his vehicle under control and to keep a reasonably careful lookout so as to avoid a collision with other persons and vehicles using the road. Black v. Gurley Milling Co., Inc., 257 N.C. 730, 127 S.E. 2d 515 (1962). The evidence in plaintiff’s favor was sufficient to permit the jury to find, on proper instructions, that the deceased’s Volkswagen was across the center line in the southbound lane, stalled and “sitting still”, when the defendant truck driver reached the north driveway some 395 feet away; that at that time it should have been apparent to the operator of the truck that the occupants of the motionless car could not save themselves; and, at that time, that the truck driver (1) could have avoided colliding with the Volkswagen by stopping or driving off the road onto the shoulder of the highway but failed to do so, or (2) would have been able to avoid the car but deprived himself of the opportunity by his failure to maintain a lookout. Since the evidence was sufficient to invoke the principle of last clear chance, the trial court erred in *451refusing, upon plaintiff’s request, to include an instruction on this issue in its charge.
 Defendants contend that even if the omission of a last clear chance instruction by name was error, it was harmless because the instruction given amounted, in substance and effect, to a charge on that issue. The specific allegations against defendants upon which the trial court charged included (1) failure to keep a proper lookout; (2) failure to keep the truck under proper control; (3) exceeding a reasonable and prudent speed under the circumstances in violation of G.S. 20-141(a); (4) exceeding the posted speed limit; and (5) failure to reduce speed to avoid a collision. The trial court also properly instructed the jury that if they found “that the plaintiff’s intestate was also negligent, con-tributorily negligent, . . . the plaintiff then would not be entitled to recover any sum whatever of the defendants” on the theory of defendants’ negligence. Although the charge covered the specific negligent acts alleged by plaintiff, at no point did the court inform the jury that even if plaintiff had been contributorily negligent, he nonetheless was entitled to recover if defendant, having the ability to avoid the injury, had failed to exercise reasonable care to do so. These instructions, consequently, were not a complete explanation of the doctrine of last clear chance and did not cure the trial court’s error in refusing the requested charge on this issue.
 As noted earlier, the Court of Appeals held that the jury verdicts on the issues submitted mooted the erroneous omission of the requested instruction. The pertinent issues submitted and the jury’s answers were as follows:
“1. Was Mary Lynn Cockrell killed as a result of the negligence of the defendant, Johnny Harold Cavanaugh?
2. Did Mary Lynn Cockrell by her own negligence contribute to her death?
The Court of Appeals regarded “the jury’s verdict finding Cavanaugh not to be negligent” as mooting this assignment of error. 32 N.C. App. at 173-174, 231 S.E. 2d at 178.
*452The jury’s answer to one issue which determines the rights of a party may render exceptions concerning other issues moot. Welch v. Jenkins, 271 N.C. 138, 155 S.E. 2d 763 (1967). “However, error relating to one issue may not be disregarded when it is probable that it affected the answer to another.” Nello L. Teer Company v. Dickerson, Inc., 257 N.C. 522, 533, 126 S.E. 2d 500, 508 (1962).
A close examination of the first issue submitted here reveals that the jury did not find that the operator of the truck was not negligent, but merely that the deceased was not “killed as a result of the negligence of . . . Cavanaugh.” (Emphasis added.) It is equally plausible that the jury’s verdict reflects a determination that the negligence of the truck driver, if any, was not the proximate cause of the death of the deceased. The jury indeed may have found that the truck driver was negligent, but that the demise of plaintiff’s intestate did not “result” from that neglect. The trial court instructed the jury that plaintiff should recover nothing of defendants should it be found that the contributory negligence of the deceased, if any, was a proximate cause of the collision. The jury therefore may have been misled to believe that a determination that the deceased’s negligence was a proximate cause of the accident precluded a finding that her death resulted from the negligence, if any, of the truck driver. The fact that the jury answered the first issue “No” and the second issue “Yes”, despite having been charged at three separate times to skip the second issue if the first issue was answered in the negative, evidences some degree of confusion on the jury’s part in this regard. The erroneous refusal to instruct the jury that, under the doctrine of last clear chance, the truck driver’s negligent acts, if any, could have been the efficient proximate cause of the deceased’s death despite her having been contributorily negligent may have affected the jury’s determination of the first issue; consequently, the jury’s answer to that issue did not cure the trial court’s error in omitting a charge on last clear chance.
The jury should have been allowed to consider the issue of defendant’s negligence in light of a proper instruction on the doctrine of last clear chance. Moreover, although no assignment of error has been brought forward concerning these matters, there may be a serious question as to the sufficiency of the evidence to require the submission to the jury of the contributory negligence *453issue and defendant’s counterclaims. Plaintiff’s evidence tends to show that the defendant truck driver need only have swerved his vehicle to the right in order to have avoided the collision entirely.
 Plaintiff contends in his second assignment of error that the trial court should have admitted the opinion evidence of Ricky Vann Williams as to the speed of defendant’s truck immediately prior to the collision. Williams testified that he did have an opinion as to the speed of the tractor tanker but the trial court sustained defendant’s objection to admission of that opinion. Because Williams’ answer to the question was not preserved in the record, we have no basis for determining whether its exclusion prejudiced plaintiff. Gower v. City of Raleigh, 270 N.C. 149, 153 S.E. 2d 857 (1967). Nevertheless, since this question may recur at retrial, we note that the record, as it now stands, shows that Williams heard the vehicle approaching or clearing the top of the knoll, saw it at the “School” caution sign 750 feet from the point of impact, observed it again at the north driveway and then watched it from the time it passed him at the crosswalk until it struck the Volkswagen. The witness, on this record, had more than ample time to form an opinion as to the speed of the truck and, should he testify to substantially the same facts at retrial, his opinion of the truck’s speed should be admitted. Loomis v. Torrence, 259 N.C. 381, 130 S.E. 2d 540 (1963).
For the reasons given, the decision of the Court of Appeals is reversed and the cause remanded for further proceedings consistent with this opinion.
Reversed and remanded.