Heidi Company is considering the acquisition of a machine that costs $844,200. The machine is expected to have a useful life of six years, a negligible residual value, an annual net cash flow of $140,700, and annual operating income of $67,000. What is the estimated cash payback period for the machine (round to one decimal point)?

a.4.1 years

b.6.0 years

c.12.6 years

d.2.1 years