Two Students miss a final exam

Introductory Chemistry was taught at Duke University for many years by professor Bonk. One year, two guys took the class and did pretty well on all the quizzes and mid-terms--so much so that going into the final, they each had a solid A. These two friends were so confident going into the final that the weekend before finals week, despite the Chemistry final being on Monday, they decided to go to the University of Virginia to party with some friends.

They did this and had a great time. However, with their hangovers and tiredness, they overslept all day Sunday and didn't make it back to Duke until early Monday morning. Rather than taking the final then, they found professor Bonk after the final and explained to him how they missed the final. They told him they went up to the University of Virginia for the weekend and had planned to come back in time to study, but they had a flat tire on the way back and didn't have a spare. They couldn't fix it for a long time and were late getting back to campus.

Bonk thought this over and agreed that they could take the final the following day. The two guys, elated and relieved, studied that night and went in the next day at the time that Bonk had told them. He placed them in separate rooms and handed each of them a test booklet. He told them to begin.

They looked at the first problem which was something simple about morality and solutions; it was worth 5 points. "Cool," they thought, "this is going to be an easy final". They then turned the page. They were unprepared, however, for what they saw on it. The question contained only two words: (95 points) Which tire?