I can't find anywhere in the FAQ or rules that say a user can't ask a question if they already know the answer. I see constant references in comments and answers to this being prohibited, but, please direct me to where this is spelled out as I can't find it. Implying that because the questioner knows the answer it's not a question is a semantic game that anyone can play, but the definition of a question in the dictionary certainly doesn't say that if the asker knows the answer it's not a question. If there is going to be this sort of a prohibition, that's fine but it's unfair to close a question for this without it being in the rules somewhere.
Further, if the asker knows an answer but suspects that there might be more than one answer, but doesn't want to bias the answers by sharing that up front, it becomes perfecly reasonable to ask that question, so I don't even really understand the prohibition's motivation in the first place, if there is in fact one.