I'm reviewing RRE LR questions. I came across PrepTest February 1997 Section 1 Question 23 (the one about the professor's travel plans) in a drill. Even after blind review, I got it wrong. I know the right answer, but I don't know why it's right or why the other ones are wrong. Can someone explain it to me? I'm not sure where to even start with this one.

Admin note: Edited title. Please use the format of "PT#.S#.Q# - [brief description of question]"