A plumbing company outfits six panel vans with $5,000 of supplies each Saturday and sends them out into the field on service calls Monday through Friday where about half the supplies are used. Its warehouse, which is used to restock the vans on Saturdays, holds $20,000 of inventory, and it takes four weeks to turn it. How long does the company hold the average part? a. 5 weeks b. 4 weeks c. 7 weeks d. 6 weeks