Answer:
x = 40
Step-by-step explanation:
We know that the angles marked (x+20)º and 120º form a straight line, so they add to 180º. This means that x + 20 + 120 = 180, so x = 40.
Note: the sum of the interior angles of any triangle is equal to 180º. Another way to solve this problem would be to set (x+20) + 2x + x equal to 180 and solve for x. You would be able to solve the problem this way if you were not given that the exterior angle was 120º.
