please answer in full sentences , and show your work.

Answer:
b) ∠4 = m∠U + m∠L
∠4 = 25° + 52°
∠4 = 77°
Step-by-step explanation:
a) Exterior Angle Theorem. The measure of an exterior angle of a triangle is equal to the sum of the measures of the two non-adjacent interior angles of the triangle.