Pythagorean Triples

just use Pythagoras's theorem to work it out.  The Pythagorean triple that they gave you is irrelevant.

Hint:

Since you want the shortest side, there will be a take away.  (minus)

This is not possible in a right triangle....   the shorter side + the 20 side do not add up to more than 99 ....necessary to meet the triangle side length rule. .