The base angles are opposite the congruent sides (marked by the single tickmarks). The base angles are Angle R = 2x Angle Q = 2x
Add up the three angles, and set the sum equal to 180. Then solve for x P+Q+R = 180 40+2x+2x = 180 40+4x = 180 4x+40 = 180 4x+40-40 = 180-40 4x = 140 4x/4 = 140/4 x = 35
So the value of x is 35 which means Angle R = 2*x = 2*35 = 70 Angle Q = 2*x = 2*35 = 70
Notice how P+Q+R = 40+70+70 = 110+70 = 180 which helps us confirm the answer
