Bay of Plenty Electricity (BOPE) is an electrical utility company in the Bay of Plenty, New Zealand. BOPE has 21 company cars that the head-office employees share for company business. However, BOPE has to reduce its costs. Assuming that the average number of employees needing a car per work-hour is 4, the average time they need the car is 2.5 hours, and the average utilization of cars is desired to be 83%, how many cars does BOPE need?