text: solve the system by substitution. x - 7y = 9, 2x - 7y = 4? college algebra -7y=9-x 7y=x-9  2x-7y=4 2x-(x-9)=4 x+9=4 x=-5  -5-7y=9 -7y=14 y=-2   you can check and find that it works in both equations.  or, you could take the value you found for x and solve for y in the other equation and see if you get the same answer.  you do.  (-5,-2) is the answer.  hope this helps!