Hi Please help with this Q by showing full step and without using financial calculator:

Project X has annual cash inflows of $4,000, $5,300, $6,100, and $7,400 for the next four years, respectively and a discount rate of 10 percent. What is the discounted payback period for these cash flows if the initial cost is $6,500? What if it is $12,900? Assume cash flows occur evenly throughout the years.