Compute the payback period for each of these two separate investments: A new operating system for an existing machine is expected to cost $270,000 and have a useful life of five years. The system yields an incremental after-tax income of $77, 884 each year after deducting its straight-line depreciation. The predicted salvage value, is expected to last seven years, and will generate an after-tax income of $43,000 per year after straight-line depreciation