Because two sides of the rightmost triangle are congruent, the base angles would follow suit. This means 5x - 10 = 3x + 10. Simplifying this we get:
2x = 20
x = 10
Next, in the other triangle, we can say the same thing, the base angles would be congruent. From this we can say that the other base angle is 4y. Using the exterior angle theorem, we can say that the two angles with x terms add to 4y. This means 3x + 10 + 5x - 10 is 4y. We already know x is 10, so substituting that in we get:
