Factor 3mx-nx-3my+ny

$3 m x - n x - 3 m y + n y$

Factor out the greatest common factor from each group.

Group the first two terms and the last two terms.

$(3 m x - n x) - 3 m y + n y$

Factor out the greatest common factor (GCF) from each group.

$x (3 m - n) - y (3 m - n)$

Factor the polynomial by factoring out the greatest common factor, $3 m - n$ .

$(3 m - n) (x - y)$