4. Dairy Queen is a takeout 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. (1) What is the probability that a customer will spend an average of 3 to 6 minutes in waiting for service? (2) During the noontime rush, the arrival rate increases to one customer every 2.5 minutes. How fast does Linda have to work {i.e., how many customer does Linda have to serve per hour) to ensure that a noontime customer will not spend an average of more than 5 minutes in the yogurt shop