BOBO Van is a start-up company which develops an app to receive orders from customers and provide delivery service. It owns one single vehicle. Two workers form a crew. The whole crew, which includes both workers working as a team, is needed to complete the delivery service. On average, an order arrives every 20 minutes while it takes 15 minutes on average to complete the order. If an order arrives while the crew is working on another order, the arriving order needs to join the waiting line for service. Assume the app provide adequate quota to accommodate essentially any number of orders waiting in the line.

What is the average number of orders in the waiting line?

Group of answer choices

0.1227

0.0333

3

0.5

2.25