Question

Triangle A B C is shown with its exterior angles. Line C B extends through point D. Line B C extends to form exterior angle that is 135 degrees. Angle C A B is 75 degrees.
What is m∠ABC?

m∠ABC = 15°
m∠ABC = 45°
m∠ABC = 60°
m∠ABC = 75°

Answer 1

Extend BC through B to D makes the exterior angle at B a linear pair with interior ∠ABC, so ∠ABC = 180° − 135° = 45°.

Answer: 45°.