Answer:
B) Subtraction Property of Equality
Step-by-step explanation:
To get m∠B=77º, the problem subtracted 103º from both sides of 103º+m∠B=180º.
The Subtraction Property of Equality states that if x=y, then x-a=y-a.
In this case x=103º+m∠B, y=180º, and a=103º.
