angle1 = 4y - 9°
angle2 = 40°
angle3 = 5y°
Angle sum property
180° = angle1 + angle2 + angle3
Therefore,
180 = (4y - 9) + 40 + 5y
180 = 4y - 9 + 40 + 5y
180 = 9y + 31
180 - 31 = 9y
149 = 9y
149/9 = y
