The cash flows associated with sales of handheld refractometers (instruments that measure the concentration of an aqueous solution by determining its refractive index) are shown. Determine the cumulative cash flow through year 4 and estimate the expected number of positive, real-number i* values.

Year Revenue, $ Costs, $
1 25,000 30,000 2 15,000 7,000 3 4,000 6,000 4 18,000 12,000