Compute the payback period for each of these two separate investments: A new operating system for an existing machine is expected to cost $280,000 and have a useful life of six years. The system yields an incremental after-tax income of $80, 769 each year after deducting its straight-line depreciation. The predicted salvage value of the system is $11,000. A machine costs $210,000, has a $15,000 salvage value, is expected to last nine years, and will generate an after-tax income of $44,000 per year after straight-line depreciation