answer: Janet Wang calls Professor Webster on behalf of Ken Williams because Ken has lost his voice and cannot teach the class tomorrow, so Janet asks Webster whether he can pass back the midterm exams for Ken. Professor Webster agrees.
documents: #Person1#: Maths department, Doctor Webster speaking.
  #Person2#: Hello, Professor Webster, this is Janet Wang calling. I'm living two doors down from your teaching assistant, Ken Williams. Ken asked me to call you because he has lost his voice and can't talk to you himself.
  #Person1#: Lost his voice? Oh, what a shame! Is there anything I can do for you?
  #Person2#: Well, Ken has a class this afternoon from two-thirty to four and he won't be able to teach it, but he doesn't want to cancel it either.
  #Person1#: Want me to try to find somebody else to teach the class?
  #Person2#: No, not exactly. What he wants to do is to get someone to go in for him, just to pass back the midterm exams. He's already marked them and they are on the desk in his office. The whole thing wouldn't take more than ten minutes.
  #Person1#: His classes are two-thirty, eh? Well, I'm afraid at that time I'll be on campus anyway; so I can do it for him.
  #Person2#: Thank you very much, Professor Webster.