I Need Help with Poisson Distribution Problem!!

I don't know where to even start with this Poisson Dist. problem, can anyone help me solve this???

The Hillel Sandwich Shop specializes in delivery of sandwiches in New York's financial district. Customers phone or fax Hillel their orders, which are then delivered directly to the customer's place of business. From 11:30 a.m. to 1:00 p.m. Hillel receives an average of 180 orders, which arrive according to a Poisson process.

The time required to make a sandwich by Joe Hillel or either of his two assistants averages 75 seconds, and preparation times follow an exponential distribution. Once an order has been filled, it is given to one of five delivery persons. Delivery times also follow an exponential distribution and average two minutes.

On the average, how many minutes does it take a customer to get a sandwich delivered from the Hillel Sandwich Shop after placing an order??


TS Contributor
Looks like a problem with queuing network with two nodes - there are 3 people making sandwich which forms a M/M/3 queue to prepare a sandwich (node 1), and then enter to a queue with 5 servers to deliver (node 2).