I need help on proving

(1) prove that if B http://www.mathhelpforum.com/math-he...ab35a80a37.png A and A is countable, then B is countable

(2) prove that if B http://www.mathhelpforum.com/math-he...ab35a80a37.png A, A is infinite, and B is finite, then A\B is infinite

I don't even know where to start... THx