216.
M: Excuse me. What's the postage on this letter to New York, please?
W: How would you like to send it?
M: By registered airmail.
W: Eighty cents, please. And please write down the postal code in the mailing address. Anything else?
M: Yes. I'd like 6 postcards and 10 fifty-cent stamps, please.
W: All right. Here you are.
M: And this package is for London. Will you weigh it for me?
W: Yes, of course. This package is 10 grams overweight. You'll have to pay 50 cents extra for the overweight.

答案解析：
(1) 正确答案为C。根据postage邮费和registered airmail航空挂号信，可知，二人在邮局，因此C项正确。
(2) 正确答案为A。根据I'd like 6 postcards我要6张明信片，可知，A项正确。