C squared = a squared+ b squared (formula)
so therefore
(c longest side) (this is your x)
(a and b shorter sides).
C squared = 5 squared + 3 squared
C squared = 25 + 9
C squared = 31
Then you find the square root of c (which is just getting rid of the squared sign) and the square root of 31 And that is your answer
Hope this helps!!