Heidi Company is considering the acquisition of a machine that costs $598,000. The machine is expected to have a useful life of 6 years, a negligible residual value, an annual net cash flow of $147,000, and annual operating income of $83,068. What is the estimated cash payback period for the machine (round to one decimal point)?

a.7.2 years

b.4.1 years

c.5.0 years

d.7.5 years