The local bank has a single line for customers waiting for the next available bank teller. There are four bank tellers who work at the same rate. The arrival rate of customers follows a Poisson distribution, while the service time follows an exponential distribution. Customers arrive at the bank at a rate of about twelve every hour. On average, it takes about 15 minutes to serve each customer. Answers to 2 d.p's. (a) Calculate the probability that the bank is empty. (8) (b) Calculate the average time the customer spends waiting to be called. (4) (c) Calculate the average number of customers in in the bank. (4) (d) The average number of customers waiting to be served. (3)