How often does Susan go swimming?

M: Susan, what do you do for exercises?
W: I run and ride a bicycle every day, and go swimming once a week.
M: I used to go swimming and skating a lot in high school. But now I don’t have time.
W: That’s too bad. Exercise is really important.
M: I know. What do you enjoy doing most of all?
W: I enjoy swimming. Well, I’m going swimming tonight. Would you like to go with me?
M: OK, I’d love to.
W: Then let’s meet at eight outside the garden.