Respuesta :

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.
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