The remote interior angles of a triangle are basically the two angles that do not share a vertex with and are opposite to the exterior angle.
5. ∠1 and ∠2
6. ∠2 and ∠3
7. ∠1 and ∠3
Because the exterior angle of a triangle is equal to the remote interior angles we can set up the following equations:
8.

9.
Factorize both the numerator and denominator then equate to zero ...you'll get X
It would be: - 2 - (-10) = 5x - 12
= -2 + 10 = 5x - 12
= 8 + 12 = 5x
= x = 20 / 5
= x = 4