Question

∠ABC and​ ∠DEF ​are supplementary.

m∠ABC=138°
What is the measure of ​ ∠DEF ​?

42°
90°
​​138°
180°

Answer 1

As the angles are supplementary, their sum would be equal to 180
∠ABC + ∠DEF = 180
138 + ∠DEF = 180
∠DEF = 180 - 138
∠DEF = 42

In short, Your Answer would be Option A

Hope this helps!