Answer:
m∠B = 69°
Step-by-step explanation:
∠A and ∠B aré complementary angles meaning their measures add up to 90°
m∠A = (x + 9)°
m∠B = (7x - 15)°
m∠A + m∠B = 90°
(x + 9)° + (7x - 15)° = 90°
(x + 9)° + 7x = 90° + 15°
(x + 9)° + 7x = 105°
8x + 9 = 105°
8x = 105 - 9
8x = 96
x = 96/8
x = 12
Now use the expression of m∠B to plug in x and find the measure of b
(7x - 15)°
(7(12) - 15)°
(84 - 15)°
69°
m∠B = 69°
