In a replacement analysis for a vacuum seal on a spacecraft, the following data are

known about the challenger: 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 time, and MARR is 10% per year. What is the

economic life of this challenger?