Answer:
x = 40
Step-by-step explanation:
The exterior angle of a triangle is equal to the sum of the 2 opposite interior angles.
126° is an exterior angle of the triangle, then
x + 2x + 6 = 126
3x + 6 = 126 ( subtract 6 from both sides )
3x = 120 ( divide both sides by 3 )
x = 40
