Warren Corporation is evaluating a proposal to invest in a machine costing $74,000. The machine has an estimated useful life of ten years, and an estimated salvage value of $9,000. The machine will increase the company's net income by approximately $2,739 per year. All revenue and expenses other than depreciation will be received and paid in cash. (i). The payback period of the machine is approximately (round to the nearest whole number): Select one: a. Ten years. b. Four years. c. Five years. d. Eight years