Question

3c-3d , 7а-7b-7с , mx-my , -12x-8y+20

Answer 1

$3c-3d=3(c-d)$
$7a-7b-7c=7(a-b-c)$
$mx-my=m(x-y)$
$-12x-8y+20=-4(3x+2y-5)$