I would say, respond that you don't know the answer from the top of your head (assuming that's the case), and politely refer them to read the documentation (or experiment).

If the documentation doesn't exist, consider creating it.

If they ask same questions again and again, suggest them to take better notes.

I think complaining about it is counter-productive. Force them to do the legwork, explain that it is primarily their task to do research on a topic.