How do I solve 4x-y=-9 3x-3y=0 by elimination

4x-y=-9, so y=4x+9

replace the y in the second equation iwth 4x+9:

3x-3 (4x+9) = 0

3x-12x-27=0

-9x=27

x=-3

y=4x+9=4 * (-3) + 9=-3

First multiply the first equation by - 3, you get:-

-12x + 3y = 27

now add this to second equation

3x - 3y = 0

and you eliminate y

solve for x and substitute this value of x into equation 1 to find y.