4. In a department store, customers arrive at the rate of 30 per hour and the average service time is four minutes. The arrivals are described by Poisson distribution and the service times are exponentially distributed. The store is open 10 hours a day. They have employed three sales clerks. (a) Find (i) the average number of customers in the queue, and (ii) the average time a customer spends waiting in the queue. (b) Waiting cost is $100 per hour and service cost per sales clerk is $10 per hour. Using the values computed in 4 (a) earlier calculate the total of the daily waiting cost and the service cost each day if three sales clerks are used. What is the total daily cost? 4. In a department store, customers arrive at the rate of 30 per hour and the average service time is four minutes. The arrivals are described by Poisson distribution and the service times are exponentially distributed. The store is open 10 hours a day. They have employed three sales clerks. (a) Find (i) the average number of customers in the queue, and (ii) the average time a customer spends waiting in the queue. (b) Waiting cost is $100 per hour and service cost per sales clerk is $10 per hour. Using the values computed in 4 (a) earlier calculate the total of the daily waiting cost and the service cost each day if three sales clerks are used. What is the total daily cost