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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., , and are exterior angles of the triangle at right. Find , , and . Then find .  

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