We'll just give the sides a variable, the hypotenuse is A, the height is B and the bottom length is C A = 21 C = 15 This means the B = is 14.696938456699069 which is rounded to 15. But, this doesn't matter. As long as we know the hypotenuse and one side we can find out that x is equal to about 45.584691402807024, round this to 46. 46 degrees is the answer.
