It should be, 4x-8=2x-10 because you substitute that for y. Now you do, 4x-2x because you do the opposite of the positive 2x as you bring it to the other side. That is, 2x-8=10 now you bring the 8 to the other side. 2x=10+8 I added it because I do the opposite and it is a negative 8 so I add. 2x+18 now divide x=9 that's the answer.