Lenny, a Graduate Research Assistant, "Moonlights" at the Short Order

Short Answer

Lenny, a graduate research assistant, "moonlights" at the short order counter in the student union snack bar in the evenings. He is the only one on duty at the counter during the hours he works. Arrivals to the counter seem to follow the Poisson distribution with a mean of 8 per hour. Each customer is served one at a time and the service time follows an exponential distribution with a mean of 5 minutes.
-The manager thinks that students will go elsewhere for lunch if they have to wait more than 5 minutes. Therefore he's thinking of hiring another server to help Lenny, reducing the customer service time to 4 minutes. How long will students wait in line if Lenny gets help?