Philben Pharmaceutics must decide when to replace its autoclave. Philbens current autoclave will require increasing amounts of maintenance each year. The resale value for the equipment falls every year and the equipment has been fully depreciated. The following table presents this data. Year Maintenance Costs Resale Value 0 $0 $900 1 $300 $700 2 $400 $400 3 $500 $200 4 $600 $0 Philben can purchase a new autoclave for $3,000. The new equipment will have an economic life of 6 years. At the end of those years, the equipment will require $50 of maintenance. Philben expects to sell the machine for $1,200 at the end of 6 years. Assume the tax rate is 35%, the straight line depreciation assumed no salvage value, and the opportunity cost of capital for this decision is 10%. When should Philben replace its current machine?