Some new production machinery has a first cost of $100,000 and a useful like of 10 years. Its estimated operating and maintenance costs are $10,000 the first year, which will increase annually by $4000. The assets before-tax market value will be $50,000 at the end of the first year and then will decrease by $5000 annually. This property is a 7-year MACRS property. The company uses a 6% after tax MARR and is subject to a combined federal/state tax rate of 40%. Calculate the after tax cash flows. The spreadsheet also needs to be able to use WACC in place of a given interest rate. The spreadsheet needs to accommodate different tax rates, and must include ATCF for O&M and Depreciation and ATCFs of disposal if the equipment is sold in each of the 10 years. Combine these to Identify the optimal life.