"What do you get if you multiply six by nine" (it was if, not when; I misremembered) isn't the whole question, though. The protagonist was pulling letters out of a bag in order to extract the Ultimate Question from his brain, and after "whatdoyougetifyoumultiplysixbynine", he ran out of letters. So since 6 * 9 clearly doesn't equal 42 (not in base 10, at least), and since the universe didn't implode or anything, as was clearly asserted multiple times would happen if the Question and the Answer were both known at the same time in the same universe, I can only assume that there was more to the Question. Probably some more basic arithmetic, "in base 13", or something much more deep and profound.43 wouldn't that be 54?