I want you to do a favour for me.

我想我可以帮你一个忙。

youdao

I've come to ask you to do me a favour.

我是来请你帮我一个忙的。

《柯林斯英汉双解大词典》

Would you do me a favour and get rid of this letter I've just received?

你能帮我个忙把我刚收到的这封信处理掉吗？

《柯林斯英汉双解大词典》

Luctonians now hope local rivals Malvern can do them a favour by beating second-placed Broadstreet this weekend.

BBC: Lucs lose out at Peterborough

He would do Europeans a favour by refusing to let his commission become a retirement home for political has-beens.

ECONOMIST: President Prodi

Irish voters may do France a favour by again rejecting the Nice treaty, widely if incorrectly assumed essential to enlargement.

ECONOMIST: France and enlargement