Tickets for the new Herbinators concert went on sale last Saturday morning at the United Centre box office. Customers arrived at the United Centre at a steady rate of 300 per hour starting at 5am until noon, and a queue formed in front of the box office. There was no balking or reneging. At 9am, the box office opened and began selling tickets through 8 ticket windows, each of which served customers at a steady rate of 60 per hour. The box office closed at noon, at which point all remaining customers in line were turned away.

a) How many customers did the box office serve on Saturday morning?

b) How many customers were in line when the box office closed?

c) How many customers were in line when the line was at its longest?

d) What is the inventory build-up graph?