9.2.3 Customers arrive at a checkout station in a market according to a Poisson process of rate  D 1 customer per minute. The checkout station can be operated with or without a bagger. The checkout times for customers are exponentially distributed, and with a bagger the mean checkout time is 30 s, while without a bagger this mean time increases to 50 s. Compare the mean queue lengths with and without a bagger.