Answer:
∠B = 48°
Explanation:
Since ∠A and ∠B are complementary angles their angles sum up to 90°.
In order to find ∠B add both ∠A and ∠B and equate them to 90° and solve for ∠B
That's
∠A + ∠B = 90
42 + ∠B = 90
∠B = 90 - 42
We have the final answer as
∠B = 48°
Hope this helps you