ok, we need to factor the expression
[tex] {y}^{5} - 2 {y}^{4} - cxy + 6x = {y}^{4} (y - 2) - x(cy - 6)[/tex]
since the expression divisible by y-2, then
[tex]cy - 6 = k(y - 2)[/tex]
since 6=2k, then k=c=3
