A company is considering the purchase of a new machine for $48,000. Management expects that the machine can produce sales of $16,000 each year for the next 10 years. Expenses are expected to include direct aterials, direct labor, and factory overhead totaling $8,000 per year plus depreciation of $4,000 per year. All revenues and expenses except depreciation are on a cash basis. The payback period for the machine is?