Demand for an item occurs according to a Poisson distribution with mean 3 a day. The maximum stock level is 25 items, which occurs on each Monday, immediately after a new order is received. The order size thus depends on the number of units left at the end of work week on Saturday (the business is closed on Sundays). Determine the following: (a) The average weekly size of the orders (b) The probability of incurring shortage in demand after 4 working days. (c) The probability that the weekly order size will exceed 5 units.