The number of players of an online game triples each week. the function f(x) = 3^x represents the number of players in week x. when are there 81 players?

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.