A: How much does that pen cost?
B: It costs ten dollars.
A: That's very expensive. Do you have anything cheaper?
B: Sure. This pen is only two dollars.
A: Good. I'll take it.
A: How much is this book?
B: It's seven dollars.
A: Do you have change for a hundred?
B: No problem.
A: OK. Here's the money.
B: Thank you. Here's the book and your change.