Confused by your "a0inches" thing.
Anyways, first off, here's a nifty idea, "Pythagorean's theorem," if you haven't heard of it, great, here it is. Say the sides of the right triangle are "a" and "b," and the hypotenuse is "c," the hypotenuse of any right triangle is the square root of: a^2 + b^2. Thus, 72 + 72, equals 144, and we have to root 144 to get the hypotenuse, so the hypotenuse is 12.