Compute the payback period for each of these two separate investments:

A new operating system for an existing machine is expected to cost $240,000 and have a useful life of six years. The system yields an incremental after-tax income of $69,230 each year after deducting its straight-line depreciation. The predicted salvage value of the system is $9,000.

A machine costs $180,000, has a $13,000 salvage value, is expected to last seven years, and will generate an after-tax income of $38,000 per year after straight-line depreciation.