2x 3y = 1200. Subtract 2x from both sides: 2x -2x 3y = 1200 -2x
Now Divide both sides by the number next to y. In this case 3: 3y/3 = 1200/3 -2x/3
Now we're left with y = 400 -2x/3
Move variables to the left y = -2x/3 400.
Hope I helped, and good luck!(: