(y-4)(y+2)-(y-2)^2=-30

(y -4)(y+2) -(y -2)² = -30

y² -2y -8 -(y² -4y +4)= -30

y² -2y -8 -y² +4y -4 = -30

2y -12 = -30

2y = -30 +12

2y = -18

y = -18/2

y = -9