Answer:
y = 40
Explanation:
in the triangle , AB = AC ( indicated by dashes through the sides )
Then the triangle is isosceles with base angles congruent (equal ), then
∠ B = ∠ C = 40°
The sum of the 3 angles in the triangle is 180°
sum the angles, equate to 180 and solve for y
∠ A + ∠ B + ∠ C = 180 ( substitute values )
2y + 20 + 40 + 40 = 180 ( simplify left side )
2y + 100 = 180 ( subtract 100 from both sides )
2y = 80 ( divide both sides by 2 )
y = 40