ANSWER:
x=0
STEP BY STEP EXPLANATION:
1.) 12x-5y=-20
y=x+4
2.) 12x-5(x+4)=-20
*because you are taking the y= equation and putting that into 5y replacing the y.
3.) 12x-5x-20=-20
*because you multiply -5 by the x and the 4 and get -5x-20.
4.) 7x-20=-20
*because you subtract 5x from 12x because you are using like terms to make the equation smaller.
5.) 7x=0
*because you add the 20 on both sides to cancel out the 20 to get x closer to being by itself.
6.) x=0
*because you divide 7 on both sides to get x completely by itself.