Angles in a triangle always add up to 180, so you could write an equation to solve for x: 31 + x + 4 + 3x + 9 = 180 44 + 4x = 180 - 44 4x = 136 ÷ 4 x = 34 So now that you have the value of x, you can use substitution to find angles S and T. 34 + 4 = 38° = angle S 34 × 3 = 102 102 + 9 = 111° = angle T
