there is a Theorem: An exterior angle of a triangle is equal to the sum of the opposite interior angles.
so you have two angles that will be equal to eachother because of the tick marks on the triangle.
2x + 2x = 6x -50
4x = 6x -50 combine like terms across equal sign
-2x = -50 divide
x = 25
your angle (2x) now substitute in 25 for x.
2 * 25 = 50
