I'm not really sure what I'm supposed to do with this question in my Engineering Economics class.

Phillips Refining plans to expand capacity by purchasing equipment that will provide additional smelting capacity. The cost of the initial investment is expected to increase by $3.8 million per year after the expansion. If the company's MARR is 18% per year, how long will it take for the company to recover its investment? Identify the engineering symbols involved and their values.