CPM Homework Help : GC Problem 7-84

Three rays intersect each other to form a triangle. Each ray extends past a vertex, creating an interior & external angle on the ray, angles labeled as follows: internal, 48 degrees, external a, internal, 72 degrees, external, b, internal, unlabeled, external, c. $∠a$ , $∠b$ , and $∠c$ are exterior angles of the triangle at right. Find $m∠a$ , $m∠b$ , and $m∠c$ . Then find $m∠a+m∠b+m∠c$ .

Hint:

How do the angles within a triangle relate to each other? How do the exterior angles relate to those within the triangle?