∠ a: x
∠ b: x
∠ c: x + 21
∠ d: x - 53
∠ a + ∠ b + ∠ c + ∠ d = 360 sum of the angles of a rectangle is 360°
(x) + (x) + (x + 21) + (x - 53) = 360
4x - 32 = 360
4x = 392
x = 98
∠ c: x + 21 = (98) + 21 = 119
∠ d: x - 53 = (98) - 53 = 45
Answer: ∠ a = 98°, ∠ b = 89°, ∠ c = 119°, ∠ d = 45°