Equals 180 because the exterior angle in question is equal to the sum of the other two angles in the triangle. In other words, the other two angles in the triangle (the ones that add up to form the exterior angle) must combine with the angle in the bottom right corner to make a 180 degree angle.
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Add whole numbers.
2x + 1 + 37 + 118 = 180
Add whole number (if there is any).
2x + 38 +118 = 180
Subtract 156 from both sides to have one side have a variable.
2x + 156 = 180
-156 -156
Divide both sides by 2 because you don't need the whole number with the variable.
2x = 24
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2 2
You get the answer as 12.
x = 12
Check:
2(12) + 1 + 37 + 118 = 180
24 + 1 + 37 + 118 = 180
25 + 37 + 118 = 180
62 + 118 = 180
180 = 180
