PTF97.S1.Q23 - This semester Professor Popkin will...

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.

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