An investment project has annual cash inflows of $2,800, $3,700, $5,100, and $4,300, for the next four years, respectively. The discount rate is 9 percent. What is the discounted payback period for these cash flows if the initial cost is $5,200? What if the initial cost is $6,400? What if it is $10,400?

Please answer and show work. If you can do it without excel and show me the steps I would appreciate that!