Answer:
Payback = 5.25 years
Explanation:
If a project has equal annual cash-flows, the payback period can be easily calculated using the formula:
[tex]Payback=\frac{CostOfMachine}{AnnualCashflows}[/tex]
The question does not make specific reference to cash-flows from the project, but the reduction in operating costs every year resulting from the acquisition of this machine is treated as an increase in net cashflows before taxes for the company, and as such will be used as the cash-flows for capital investment analysis.
As such:
[tex]Payback=\frac{84000}{16000}=5.25years[/tex]