Answer:
y = 48
Step-by-step explanation:
the exterior angle of a triangle is equal to the sum of the 2 opposite interior angles.
3y + 12 is an exterior angle of the triangle , so
3y + 12 = y + 30 + y + 30 ( base angles of an isosceles Δ are congruent )
3y + 12 = 2y + 60 ( subtract 2y from both sides )
y + 12 = 60 ( subtract 12 from both sides )
y = 48
