>If the answer is supposed to be integer, the simplest explanation I can think of is there is a misprint in the question. For example, if the first "known" column was 40/60 instead of 50/60 then X would be 27. Or if the known "result" value was 180 instead of 18, then X would be 216.
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>Or maybe this is a *purposeful* "mistake". Getting kids scratching their heads over this probably reinforces the learning. Perhaps kids who point out the problem get extra credit?

Bingo. I had our girl write down the answer of 21.6, showing how we arrived at it. She and one other kid in the class came up with the right answer. There wasn't any intention on the teacher's part to do this, but she admitted that all other problems on the worksheet solved with integers except that one, and she wasn't sure why. So, I think it was a misprint, and though unintentional, she got points with the teacher for not giving up on it. Good call!