a machine purchased three years ago for $720,000 has a current book value using straight-line depreciation of $400,000; its operating expenses are $60,000 per year. a replacement machine would cost $480,000, have a useful life of nine years, and would require $26,000 per year in operating expenses. it has an expected salvage value of $130,000 after nine years. the current disposal value of the old machine is $170,000; if it is kept 9 more years, its residual value would be $20,000.