I cannot figure this question out:

A straight length of wire is 20cm long. It is bent at right angles to form the two shorter sides of a right angled triangle. If the triangle's area is 30cm squared, find:

a). the length of the hypotenuse

b) the triangle's perimeter

My logic went like this:

a squared + b squared = c squared

therefore if 20 is a+b

20 squared = csquared, and

20 = c

That was incorrect and I have no idea how to do the problem