two alternative machines are being considered for a manufacturing process. ⚫ machine a has an initial cost of $75,200, and its estimated salvage value at the end of its six years of service life is $21,000. the opening costs of this machine are estimated to be $6,800 per year. extra income taxes are estimated at $2,400 per year. ⚫ machine b has an initial cost of $44,000, and its salvage value at the end of its six years of service life is estimated to be negligible. its annual operations costs will be $11,500. compare these two alternatives by the present-worth method at i