Pizza Milano is a popular pizza restaurant in Almere, Netherlands. In addition to a prospering eat-in business it also has a flourishing delivery business. On average, PM's delivery business receives orders at a rate of 7.9 per hour. To fill an order, PM first bakes the pizzas and assembles the order (this takes exactly 14 minutes without any uncertainty), then a delivery person on a motorcycle takes the order to the customer (8 minutes on average), drops off the order (3 minutes) and returns to the restaurant (8 minutes). The total time a delivery person spends on an order follows an Exponential distribution. What is the minimum number of delivery persons needed to keep up with the demand for deliveries?