By the Isosceles Triangle Theorem, if two sides of a triangle are congruent, then the angles across from those sides are also congruent. So angle A = angle B. 2x-20=x+8. Simplifying that gives us x = 28. That means that B = 28+8 which is 36. Both A and B are 36°. First choice. For angle C, by the Triangle Angle-Sum Theorem, all the angles of a triangle equal 180. Therefore, angle C = 180-36-36 which is 108°. Second choice.