On a map of the Fox River, 1 centimeter represents 4 kilometers. If a trail by the river is actually kilometers long, what is the length of the river on the map

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.