Please explain the conversion process of getting Nu =48 from 1min and 15 seconds. I understand Lambda is 39.5. Thank You that is the only piece I need help with

The local coffee shop has 2 employees, one takes the orders and then takes payment, and the other worker makes the coffee drinks. While some folks ask for a simple cup of coffee that just needs to be poured, others ask for more elaborate coffee drinks, and others order multiple drinks. On average, though, it takes a total of 1 min and 15 seconds to process a customer, take the order, make the payment, and make the drink(s). During the busiest time of the day, 7:30am to 9:30am, about 39.5 customers come in per hour: 1. (2 POINTS) Since the two workers only service one customer at a time, they are in fact working like a single worker. What percentage of the time is this single team of workers busy? 2. (2 POINTS) What is the average time a customer waits before they place an order? (In minutes) 3. (2 POINTS) What is the average number of customers in the line