x/2 +3y = 6 . . . . . . . . starting point
x/2 = 6 -3y . . . . . . . . subtract terms that don't have x
x = 2(6 -3y) . . . . . . . . multiply by the inverse of the x-coefficient
x = 12 -6y . . . . . . . . . expand if you like
3y = 6 -x/2 . . . . . . . . subtract terms that don't have y
y = (6 -x/2)/3 . . . . . . . multiply by the inverse of the y-coefficient
y = 2 -x/6 . . . . . . . . . expand if you like