A Flower Shop Has One Employee in the Front of the Store

Essay

A flower shop has one employee in the front of the store to sell flowers out of a cooler. On Saturdays customers arrive every six minutes, on average. The employee can serve a customer every five minutes, on average. The owner of the store feels that if there are more than four customers in the store at one time, additional customers may not come in because the wait appears too long.
a. What is the chance of four or more customers being in the store at one time?
b. What is the total time (in minutes) a customer spends in the store?
c. What is the average number of customers in the store?