I could use a hand with this

An investment project has annual cash inflows of $3,900, $4,800, $6,000, and $5,200, for the next four years, respectively. The discount rate is 15 percent. a. What is the discounted payback period for these cash flows if the initial cost is $6,600? (Do not round intermediate calculations and round your answer to 2 decimal places, e.g., 32.16.) b. What is the discounted payback period for these cash flows if the initial cost is $8,700? (Do not round intermediate calculations and round your answer to 2 decimal places, e.g., 32.16.) C. What is the discounted payback period for these cash flows if the initial cost is $11,700? (Do not round intermediate calculations and round your answer to 2 decimal places, e.g., 32.16.) a. years b. Discounted payback period Discounted payback period Discounted payback period years C. years