Answer:
137
Step-by-step explanation:
First start with what you know. The measure of the interior angles of a triangle total to so 51 + 2x + x = 180, then 51 + 3x = 180, 3x = 129, so
x = 43, the exterior angle is on a straight line with x so
x + exterior angle = 180 [since they are supplementary], since x = 43 then
43 + e = 180, so e has to be 137