PLEASE HELP ME IM HAVING TROUBLE WITH THIS PROBLEM!! Kenner and his friends went to the store and bough 2 bags of candy for $21 each. They decided to split the bill in 1/3. How much money did Kenner pad?

Let x have probability generating function gx (s) and let un generating function u(s) of the sequence uo, u1, satisfies p(x > n). show that the (1- s)u(s) = 1 - gx(s), whenever the series defining these generating functions converge.