could you help me what will be the most natural way to say in this conversations?

A: Would you do me a favior?

B: What is it? Tell me?

A: You first say YES, and I will tell you.

B: Hmm, there must be something going on. Let me first listen please?

A: Ok,,, I have a party tonight, would you be a my one night partner please?

B: Sorry but that's a bit hard for me.

Many thanks~