geometry
posted by Mary .
The surface area of a rectangular prism is 190 square inches, the length is 10 inches, and the width 3 inches. Find the height.
I know how to do SA but I don't understand how to find height if you have SA given. The answer is 5 in but I am not able to come up with the right answer.

let the missing dimension be x in
SA = 2(10)(3) + 2(10)(x) + 2(3)(x)
190 = .....
solve for x