Chemistry at Duke

  Introductory Chemistry at Duke University has been taught for about a
  zillion years by Professor Bonk (really), and his course is
  semi-affectionately known as "Bonkistry." He has been around forever,
  so I wouldn't put it past him to come up with something like this.

  Anyway, one year there were these two guys who were taking Chemistry
  and who did pretty well on all of the quizzes and the midterms and
  labs, etc., such that going into the final they had a solid A.  These
  two friends were so confident going into the final that the weekend
  before finals week (even though the Chem final was on Monday), they
  decided to go up to UVirginia and party with some friends up there.

  So they did this and had a great time.  However, with their hangovers
  and everything, they overslept all day Sunday and didn't make it back
  to Duke until early monday morning.  Rather than taking the final then,
  what they did was to find Professor Bonk after the final and explain to
  him why they missed the final.  They told him that they went up to UVa
  for the weekend, and had planned to come back in time to study, but
  that they had a flat tire on the way back and didn't have a spare and
  couldn't get help for a long time and so were late getting back to
  campus.

  Bonk thought this over and then agreed that they could make up the
  final on the following day.  The two guys were elated and relieved.
  So, they 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 and told them to begin.  They looked at the
  first problem, which was something simple about molarity and solutions
  and was worth 5 points.  "Cool" they thought, "this is going to be
  easy." They did that problem and then turned the page. They were
  unprepared, however, for what they saw on the next page.  It said:

                  (95 points)  Which tire?