The answer is: 18° . __________________________________________________ Explanation: ________________________________ x + 4x = 90 ; solve for "x" ____________________________ 5x = 90 ; ____________________________ Divide EACH SIDE of the equation by "5"; to isolate "x" on one side of the equation; and to solve for "x" ; ___________________________________________________ 5x / 5 = 90 / 5 ; ___________________________________________________ x = 18 ; The answer is: 18° . _____________________________________________________