What’ s David’ s problem?

M: Maths Department, Doctor Winston speaking.
W: Hello, Prof. Winston. This is Eliza Smith calling, I’m living two doors down from your teaching assistant, David Williams. David asked me to call you because he lost his voice and can’t talk to you himself.
M: Lost his voice? Oh, what a shame! Is there anything I can do for him?
W: Well, he has a class this afternoon from 2:30 to 4:00 and he won’t be able to teach it, but he doesn’t want to cancel it either.
M: Want me to try to find somebody else to teach the class?
W: No, not exactly. What he wants to do is to get someone go in for him, just to pass back the mid-term 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.
M: His class is at 2:30, eh? Well at that time I am going to be on campus anyway; so I can do it for him. What room is his class in?
W: Building 4, room two fourteen. Will you need his office key to get the exams? He’s given it to me and I could bring it to you.
M: Actually, that won’t be necessary. We have a master key in the maths department. So I can get into his office if necessary.
W: Thanks very much, Prof. Winston. David doesn’t have another class to teach until Tuesday, and hopefully, he will be able to talk by then. He’ll call you as soon as he can. Oh, yes, I almost forgot. Could you put the next assignment, on the board, too? It’s all the problems on page 45, and they are due at the next class.
M: No trouble at all. Thanks for passing all the news about David, and please tell him not to worry about anything.