Answer:
y = 40
Step-by-step explanation:
it is an isosceles triangle BA = BC and angle B = angle C.
the sum of the internal angles (in a triangle) is 180°, take away the 2 know angles and you will have angle A
180 - 40 - 40 = 100° (angle A)
now we know that 100 = 2y +20 (angle A)
solve
100 = 2y + 20
80 = 2y
y = 40
-------------------------
check
40 + 40 + 2 * 40 + 20 =
180°
The answer is good
