Answer: ∠B = 82°
Step-by-step explanation:
To find the measure of B, you have to find the measure of A.
m∠143° + m∠A = 180° because they are a linear pair
m∠A + 143 = 180
Subtract both sides by 143
m∠A = 37
Since you know the measure of angle A, you can find angle B
Angle A, B, and C should add up to 180° as triangles' angles sum up to 180°.
∠B + ∠A + ∠C = 180°
Substitute
∠B + 37 + 61 = 180
∠B + 98 = 180
Subtract 98 from both sides
∠B = 82°
