4. [10 marks] An upscale coffee shop has two employees. Customers line up to wait for the first available employee, however if there are 4 or more customers already in the store (either being served by an employee or waiting in line), no-one else will join the line. The customer's average arrival rate also varies according to how many customers are already waiting (see table below). Each employee can help customers at a rate of 10 per hour. a) Sketch the appropriate model. b) What is the steady state probability of having 0,1,2,3 or 4 customers in the shop? c) How many customers are in the shop (waiting or being served) on average? d) What is the average time that a customer spends in the shop (total of waiting time and service time)