The following data are known. The initial investment is $12,000; there is no annual maintenance cost for the first three years, however, it will be $2,000 in each of years four and five, and then $4,500 in the sixth year and increasing by $2,500 each year thereafter. The salvage value is $0 at all times, and the MARR is 10% per year. What is the economic life of this challenger?

	a.	4 years
	b.	5 years
	c.	1 year
	d.	3 years
	e.	2 years

choose one