please explain how to solve this question

5.5 Consider a project with the following cash flows: End of Year (n) Cush Flows ($) 0 1 2 3 4 5 6 $22,400 4,500 12,670 14,780 13,650 11,440 7,800 (a) At an interest rate of 18%, what is the discounted payback period? (b) What is the discounted payback period if the interest rate is 0%