The tool crib at a large manufacturing company is responsible for providing tools to the factory workers on demand. The tool crib has a variable demand.​ Historically, its demand has ranged from 320 to 570 small tools per day with an average of 445. Diane, the tool crib​ attendant, works eight hours a​ day, five days a week. Each order is for one small tool and each small tool takes Diane 1 minute to retrieve from the bins.

What is the average waiting​ time, in​ minutes?

6.4， 5.4， 7.4， 1？