Customers arrive at a tool crib according to a Poisson process of rate λ = 5 per hour. There is a single tool crib employee, and the individual service times are random with a mean service time of 10...

Customers arrive at a tool crib according to a Poisson process of rate λ = 5 per hour. There is a single tool crib employee, and the individual service times are random with a mean service time of 10 minutes and a standard deviation of 4 minutes. In the long run, what is the mean number of workers at the tool crib either being served or waiting to be served?