geometric distribution...p.g.f

hi can any one help with this prblem

Items are bought by individal customers entering a shop and the number of items is a random variable X which has a geometric distribution starting at 0 and has a mean of 4/6.

what is the value of the parameter p of the geometric distribution and what is the p.g.f.(probability generating function ) function of X.

if four customers then visit the shop what is the probability generating function of Y the total amount of items they buy( all items bought are independent of each other 0.

any help , thanks...