Answer:
see below
Step-by-step explanation:
1. < 4 is the exterior angle of a triangle given
2. <1 + <2 + <3 =180 basic property of triangles
3. <3 + <4 are a linear pair <3 and <4 are adjacent and form a straight line
4. <3 and <4 are supplementary angles supplementary angles are linear pairs
5. <3 + <4 = 180 The definition of supplementary angles are that they add to 180 degrees
6. <1 + <2 + <3 = <3+ <4 Substitute <3 + <4 for 180 in equation from step 2
7 <1 + <2 = <4 Subtract <3 from each side using the subtraction property of equality
