The ticket center at the Stadium where the team play minor league baseball uses a multiple channel queuing system, as fans arrive, they wait in a single file line for the next available ticket window. On average, it takes 2 minutes to purchase a ticket and fans arrive at the ticket booth at an average rate of 7 customers every five minutes, find the following:

a. The minimum number of ticket windows that must be open to allow for a feasible system.

b. When three ticket windows are open, what is the average number of fans waiting in line? 

c. When four ticket windows are utilized, what is the probability all windows are empty? 

d. When four ticket windows are utilized, what is the average time a fan waits in line?

e. When five ticket windows are utilized, what is the average number of fans waiting in line?