This is a question taken out of my grade 12 math textbook, which I am having difficulty solving. Though, I have a feeling I am just missing something that should be really obvious. I'd appreciate if someone could help me figure out what steps I have to take in order to solve the problem!

A right triangle has an area of 25 cm squared. Express the hypotenuse, h, of this triangle as a function of it's perimeter, p. Hint: consider the square of the perimeter.

Theanswer, taken out of the back of my textbook, is:

h(p) = (p squared - 100)/2p