x=2 y=1--The following expression is to be simplified: x(2x-y)-x(x-y)-y(x+2y)

My book's answer to the above isx^2-xy-2y^2

Can somebody show me, step by step, how that answer was derived. I've been working on it for nearly an hour now and still haven't got it!

Thanks for your help, guys.

EDIT: Specifically, how does the 'x' variable get cancelled out? (The one on the first line.) I don't get why it's 2y^2 and not 2xy^2