72y-54y=18y
12x2y3-27x2y=3x2y(4y2-9)=3x2y(2y+3)(2y-3)
=3X2y(4y2-9) =3X2y(2y+3)(2y-3)
3X2Y*(2Y+3)*(2Y-3)
3x2y(2y+3)(2y-3)