Why did Rock come into the room?

W: Come in, please.
M: Hello, Roy. Where’s Alan? I want her to type this letter for me.
W: I’ m afraid she can’t, Rock. She isn’t working today.
M: Oh, why? Is she ill?
W: No. She’s preparing for an exam.
M: An exam? Is she going to school?
W: Yes, she is. She’s learning Japanese in night school.
M: I see. Are you going to night school, too?
W: No, I’ m not, not this year. But I’ m thinking about taking a course next year.
M: That’s a good idea. Is it expensive?
W: No, not very. Anyway, it’s worth it.