Answer:
70°
Step-by-step explanation:
(a) Calculate the value of x
∠A + ∠B + ∠C = 180
40 + 2x - 30 + x + 20 = 180
Combine like terms
3x + 30 = 180
Subtract 30 from each side
3x = 150
Divide each side by 3
x = 50
(b) Calculate m∠B
m∠B = 2x - 30 = 2×50 - 30 = 100 - 30 = 70°
