12) (8y + 6)(1,8 – 0,4y) = 0

8y + 6 = 0 or 1.8 - 0.4y = 0

8y = -6 => y = -6/8 = -3/4

1.8 = 0.4y => y = 1.8 / 0.4 = 18/4 = 9/2

y = -3/4 or y = 9/2