The Sorensen Supplies Company recently purchased a new delivery truck. The initial cash outflow for the new truck is $22,500, and it is expected to generate after-tax cash flows of $7,200 per year. The truck has a 5-year expected life. The expected year-end abandonment values (after-tax salvage values) for the truck are given below. The company's WACC is 9%.

Year	Annual After-Tax Cash Flow		Abandonment Value
0	($22,500)			-
1	7,200			$16,500
2	7,200			13,000
3	7,200			11,000
4	7,200			6,000
5	7,200			0

1. What is the truck's optimal economic life? Round your answer to the nearest whole number.

   _____ year(s)