(x-y)-4(2x-3xy)=x-y-8x+12xy=12xy-7x-y
(x-y)-4(2x-3xy)=x-y-8x+12xy12xy-7x-y
x-y-8x+12xy=12xy-7x-y
=x-y-8x+12xy=12xy-7x-y