BM Company wants to purchase a new machine for $40,000. In order to install the new machine BM will incur $6,000 in installation costs. BM projects that the new machine will decrease operating costs by $8,000 (cash flow basis) per year. What is the payback period for this investment by BM? Just provide the number (numeric form). Do not spell out your answers and do not include the word-- years; example 2.