6. Pizza Unlimited sells two franchised restaurant models. Model A has a capacity of 20 groups of customers, and model B can seat 30 groups. The monthly cost of operating model A is $12,000 and that of model B is $16,000. An investor wants to set up a buffetstyle pizza restaurant and estimates that groups of customers, each occupying one table, arrive according to a Poisson distribution at a rate of 25 groups per hour. If all the tables are occupied, customers will go elsewhere. Model A will serve 26 groups per hour, and model B will serve 29 groups per hour. Because of the variation in group sizes and in the types of orders, the service time is exponential. The investor estimates that the average cost of lost business per customer group per hour is $15. A delay in serving waiting customers is estimated to cost an average of $10 per customer group per hour.

(a) Develop an appropriate cost mode.

(b) Assuming that the restaurant will be open for business 10 hours a day, which model would you recommend for the investor?