Yes, they are all grammatically correct, but that doesn't mean you should use them. In my opinion, your use of question twice is repetitive, and said the answer sounds awkward. ), but I can provide suggestions.
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vcolts"I have already answered this in a previous question" is also acceptable, right? (If I am not refering to a question right before the one I am talking about)Yes, perfectly fine.
vcoltsAlso, even if it's repetitive to repeat question twice, if it's a formal setting (an exam/presentation), isn't it better to repeat it?