PLEASE HELP!2. In the figure, is an exterior angle to < LAU.A-Explain why is equal to the sum of the measures of the two nonadjacent interior angles.B- What is?

Same question was posted earlier .... I repeat my answer here ...

Question (2a):
Given that sum of triangle = 180°
∠1 + ∠2 + ∠3 = 180°
∠3 = 180° - ∠1 - ∠2     ---------------- (1)

Given that sum of angles on the adjacent line = 180°
∠3 + ∠4 = 180° 
∠4  = 180° - ∠3 ------------------------(2)

Sub (1) into (2)
 ∠4  = 180° - (180° - ∠1 - ∠2 ) 
∠4  = 180° - 180° + ∠1 +∠2  
∠4  =  ∠1 +∠2  (proven)

Question (2b):
∠4  =  52° + 25° 
∠4  =  77°