At a catalog order centre for gardening supplies, customers browse catalogs, look at display items, and fill out an order card for items that they wish to purchase. They then join a single queue and wait to be served by the next of the six clerks who becomes available (arrivals follow a Poisson process with an average arrival rate of 49 customers per hour.) Clerks will then take the customer’s order card, enter the order in the computer, retrieve the items from a small warehouse, and process payment. Studies show that the service time follows a negative exponential distribution with an average time of 4.11 minutes per customer. What is the average amount of time from when a customer joins the queue until they are finished being served, in minutes? (in minutes)?

a. 0.0041 mins

b. 0.19 mins

c. 2.36 mins

d. 4.34 mins