I think you can ask for whatever you like. It's your responsibility to be able to determine how much help is reasonable (as far as without payment goes).
If the assignment is easy, and nothing very specific, you can probably just paste the whole thing and someone will do it. If it is more difficult/requires higher education/more experience, your chances of someone doing it for you are lower.
If you've got a question on ANYTHING academic related you should just post it here.
If you want people to do assignments or essays for you there are a few people that would gladly do it for you, however for the most part they do charge.
However for basic stuff such as questions on assignments, clarifications, spell checks, people, myself included would gladly assist you for free.