Answer:
Step-by-step explanation:
D. 123°
The sum of the entire interior of the triangle is 180°
A straight line is 180° as well.
Let's say that the unlabeled angle is x.
63° + 60° = 123°
180° - 123° = 57°
x = 57°
x + ∠1 = 180°
57° + ∠1 = 180°
180° - 57° = 123°
