Engineering Economics

A contractor has purchased a heavy machine for $1,500,000 that will reduce materials and labor costs by 5. 420,000 each year for N years. After N years,there will be no further need for the machine, and because the machine is specially designed, it will have no MV at any time. However, you can depreciate the equipment on an SL (Straight Line) basis with a tax life of five years. If the effective income-tax rate is 40%, what is the minimum number of years the contractor must operate the equipment to earn 10% per year after taxes on its investment? (20%)