Since the triangle has 3 equal sides, it has 3 equal angles.
If the total angle degrees is (n-2)180 = 180°
180°/3 = 60° per angle
x:
Since a straight line is 180°, 180°-60° = 120°
y:
And since for a triangle the total measure of the angles is 180° and ∠x is 120°, the equation is;
180 = 120 + y + y
60 = 2y
y = 30°