You start with the equations "2x +2y=38" and "6+x=y". By adding and subtracting in the second equation, you get "2x +2y=38" and "x-y=-6". When you multiply the second equation by 2, you get "2x-2y=-12."
subtracting the equations "2x +2y=38" and "2x-2y=-12" gets you to "4y=50", where you have to divide two sides by 4 and get "y=12.5"