Answer:
m∠B = 3°
Step-by-step explanation:
Complementary angles when combined will equal 90° in total.
∠A + ∠B = 90
m∠A = 87° {Given}
Plug in 87 for ∠A in the given equation, and solve for ∠B
87 + ∠B = 90
Isolate the variable. Subtract 87 from both sides of the equation:
87 (-87) + ∠B = 90 (-87)
∠B = 90 - 87
∠B = 3°
m∠B = 3° is your answer.
~
