(I'd be) happy to (do something).and Be happy to (do something).
I would do it with pleasure. (The something is often replaced with a description of an activity.) John: I tried to get the book you wanted, but they didn't have it. Shall I try another store? Mary: No, never mind. John: I'd be happy to give it a try. Alice: Would you fix this, please? John: Be happy to.
See also: happy