2. In a different warehouse, book orders are handled by two members of staff, A and B, who take turns to pack each orders as it arrives (this is a non-random alternation). Assume orders arrive as a Poisson process with rate A per hour, that A packs the first order, and that orders are packed instantaneously. Let Na(f) be the number of orders packed by A by time t, and let X1, X2.... be the inter-arrival times for the process {NA()). () What is the probability distribution for X.? Hint: relate the X, to the things between orders. (b) Is (NA()} n Poisson process? Explain your reasoning. [G marks)