Respuesta :

7x-21 + 3y -xy
I think that is what you're asking for
7(x-3) + y(3-x) = 7(x-3) + (-y)(x-3) --> (7+(-y))(x-3) --> (7-y)(x-3) or -(x-3)(y-7). You can check this if u distribute it because you get 7x - 21 -xy +3y = 7x - 21 +3y - xy