The hypotenuse of a right triangle is 50mm long one leg of the right triangle is 30 mm long what is the length of the other leg

The triangle you are describing is the common 3,4,5 triangle. So the side lengths are 30, 40, and the hypotenuse is 50. This comes from Pythagorean theorem 

59/96 is the ratio hope this not 100% sure though : /