Dairy Queen is a take-out yogurt shop owned by Linda Smith. Customers arrive at a rate of 20 per hour. Linda serves a customer,on the average, in 2 minutes. Assume that the arrivals and the service times are Poisson distributed and exponentially distributed, respectively.What is the probability that a customer will spend an average of 3 to 6minutes in waiting for service?

Based on previous question,during the noontime rush, the arrival rate increases to one customer every 2.5 minutes. How fast does Linda have to work to ensure that a noontime customer will not spend an average of more than 5 minutes in the yogurt shop?