Without a value of 12 in column 2, the question is plainly wrong - there isn't a single pair that would match the facts given in the question.
The most likely possibility is a simple typo error, in which the number "13" should have actually been "12".
The only other (unlikely) possibility I can think of is to try approximation. Of course, I do recognize that this is EXTREMELY unlikely, because the question clearly states "values of x and y that are jointly
consistent with the given information"
But let's say for a moment that we try to find a pair of x and y (such that x>y) to give us the nearest answer to 15 for the hypotenuse. In that case, we would have got x = 8 and y = 13, giving us the hypotenuse as 15.26.
But even in this unlikely scenario, the answers do not match the answers shown by GMAC.