随机过程的题不会，求大神

随机过程老师布置了几道题，完全不会做，求大神
1.suppose on a certain road that one out of every 4 truck is followed by another truck where as four out of every five cars are each followed by a car .Derive the proportion of cars?
2.a store keeps an inventory of k units of on item. suppose demand for item in each minute is a bernoulli variable that equals with probability p (0<p<1). As soon as the  inventory drops to zero another batch of k is brought from a nearby ware house (no delivery time) let xn be the number of units in inventory derive the steady-stste distribution of xn and its mean