Rules for being polite in westrn culture?

Amy_xuru

丹丹啊, I could only answer the one "greeting your teacher", use the same form of address with the way you usually use to call your friend. but with a Ms or Mr.

If you want to say "how are you" or "good day", I guess that's fine too.

Amy_xuru

Oh, and also the third one "3Receving a birthday"

Mr/Ms XXX
accept the with pleasure
the kind invitation of
Mr/Ms YYY to a party
at ZZZ clock
the fifth of July
(address)

this is the formal letter accepting an Invitation.

Amy_xuru

在来一个: (接上)

Dear XXX:
   I am so sorry that I cannot come to the party you are giving next saturday because of a previous engagement that evening.
   I do appreciate your asking me and hope thyat I will have the opportunity to meet you on some other occasion in the near future.

the is the informal letter declining an invitation.