W: I want to mail this letter overseas.
M: OK, Ma’am. I’ll have to weigh it first. All right, it’s not overweight. That’s 5.5 yuan for overseas mail.
W: That’s not expensive. How long does it take for a letter to get to the U. S.
M: It all depends. It usually takes four or five days.
W: That’s wonderful. It used to take more than a week when I was staying here six years ago. Well, I want to register it.
M: All right. It probably takes a little longer to get there though.
W: Yes, I know. Well, please let me have a post office box.
M: That’s OK. Fill out this form, please.
W: How much is the rent per month
M: It’s 100 yuan per year.
W: Here is the form and money.
M: OK. Here is the key for you. The number is on it. Any more requests
W: No, thank you.

How long did it take for a letter to get to the USA six years ago（）。