According to the Descartes' rule, the number of positive i* value for the following cash flow is: Year 1 2 3 4 5 6. Revenue, $ 9,000 20,000 22,000 | 30,000 36,000 40,000 Cost, $ 35,000 12,000 15,000 23,000 25,000 25,000 25,000 4 3 2 1