How many solutions does this system have? y =-3x. -9x-4y=21
one
two
an infinite number
no solution

one or seven READ DESCRIPTION

Step-by-step explanation:

y =-3x. -9x-4y=21

-9x+12x=21

3x=21

3*7=21

if you didn't mean to do a double negative then it would be one, but otherwise it's seven

c.

step-by-step explanation:

because first you have to add the 4x, 9x, and the 7x together and you get 20x and then you add the last numbers up and you get 5and then you put the subtraction sign in there and that's how you get the answer.