Zara Store sells a large number of black dress shirts. The shirts, which bear the store label, are shipped from a manufacturer in Barcelona. The manager wants to be sure that they never run out of dress shirts. The store always try to keep at least a 2 months' supply in stock. When their inventory drops below that level, the store orders another two-month supply. The shirts cost $7 each and sell for $20 each. The cost of processing an order and receiving new goods amounts to $80, and it takes three weeks to receive a shipment. Monthly demand is approximately normally distributed with mean 140 and standard deviation 27. Assume a 10% annual interest rate for computing the holding cost.

a)What value of Q and R is Zara using to control the inventory of black dress shirts?

b) What should be the performance of a (s,S) model if Zara has 50 units during the review period?

c) What could be the (s,T) model policies by using an alpha (a) of 95% and a beta (B) of 90%?