A straight line is 180°. The angles of QRT (2x + 33) and TRS (5x - 21) make up the 180° angle. So you can do:
∠QRT + ∠TRS = 180°
(2x + 33) + (5x - 21) = 180°
2x + 33 + 5x - 21 = 180 Combine like terms
7x + 12 = 180 Subtract 12 on both sides
7x = 168 Divide 7 on both sides
x = 24
Now that you found x, you can find the angles of QRT and TRS.
m∠QRT = 2x + 33
= 2(24) + 33
= 48 + 33
∠QRT = 81°
m∠TRS = 5x - 21
= 5(24) - 21
= 120 - 21
∠TRS = 99°
