In the second equation y= 1/2x -4. you take the 1/2x-4 and substitute it for y in the first equation. 3x+2(1/2x-4)= 23. So now you get 3x+x- 8=23. Now add the 3x and x together. 4x-8= 23.Now add 8 to both sides. 4x=31. Divide both sides by 4. x= 7 3/4 or 31/4 (its the same) Now take the 31/4 and put that as x in the second equation. 1/2(31/4)-4=y. 31/4-4=y. You get y=13/4 and x=31/4