A shop servers one customer at a time and provides four seats for waiting customers. If the place is full, customers go elsewhere. Arrivals occur according to a Poisson distribution with mean 5 per hour. The time to get a service is exponential with mean 20 minutes. Determine the following: a) The steady state probabilities. b) The expected number of customers in the shop. c) The probability that customers will go elsewhere because the shop is full