A special-purpose machine is being installed at a first cost of $200,000. The following table shows the expected annual operating costs, maintenance costs and salvage values for each year of service. If interest is 10% annually, what is the economic service life for this machine? Year of Service 1 2 3 4 Operation Cost for Year 20,000 30,000 40,000 50,000 60,000 70,000 80,000 90,000 100,000 110,000 Maintenance Cost for Year 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000 10,000 11,000 Salvage Value at End of Year 100,000 90,000 80,000 70,000 60,000 50,000 40,000 30,000 20,000 10,000 5 6 7 8 9 10