Solve 15/4 - 7x =9 (someone please answer )

Can (3,5 and square root 34) be sides on a right triangle?

The perimeter of a movie screen is 54 meters. the screen is 18 meters wide. how tall is it?

Offering 30 if a plus b plus c equals 68 and ab plus bc plus ca equals 1121, where a, b, and c are all prime numbers, find the value of abc. the answer is 1978 but i need an explanation on how to get that.