Answer:
Substitution Property of Equality
Step-by-step explanation:
The substitution property of equality states that if x = y, then x can be substituted in for y in any equation, and y can be substituted for x in any equation.
In this case, m∠A + m∠B in the second equation is substituted by 88°, from the first equation. This allows as to find m∠C as follows:
88° + m∠C = 150°
m∠C = 150° - 88° = 62°