Respuesta :

(-4y - x) - (3y - 9x)

-4y - x - 3y + 9x

-4y - 3y - x + 9x

-7y + 8x
Well first thing you see -4y and 3y. add +4y to both sides. And then now you have -x - 7y - 9x. Now add 9x to both -9x and -x. So you have 8x - 9y