4. If the complement of ∠1 is 80° and m∠2 = 80°, what is m∠3?

Two complementary angles equal 90.

If angle 1's complementary angle is 80, then angle 1 is 10 (90-80=10)

The three angles of a triangle need to equal 180.

Angle 3 = 180 - angle 1 - angle 2

Angle 3 = 180 - 10 - 80 = 90

Angle 3 = 90 degrees