Your boss has asked you to look into optimizing the van ownership strategy for your company. The company you work for bought a van for $54,600 for making deliveries. You expect the van to be driven 27,300 miles per year, with each mile costing you around $0.63 per mile in the first year. The operating cost per mile is expected to increase by 5% per year after the first year. The resale value of the van is expected to decrease by 20% in the first year and then by 7% per year from there on out. What is the optimal ownership period (economic life) in years assuming a MARR of 9%