Answer:
∠TRS = 40°
Explanation:
∠UTS is an exterior angle of the triangle
The exterior angle of a triangle is equal to the sum of the 2 opposite interior angles, that is
∠UTS = ∠TRS + ∠RST
9x - 15 = 3x + 16 + x + 9
9x - 15 = 4x + 25 ( subtract 4x from both sides )
5x - 15 = 25 ( add 15 to both sides )
5x = 40 ( divide both sides by 5 )
x = 8
∠TRS = 3x + 16 = (3 × 8) + 16 = 24 + 16 = 40°