Can you please help with questions a. and b. please show excel formulas

Problem 11.4: Assume you work for Stellar Solar, a manufacturer of roof-top solar panels. Stellar is considering three capital projects for next year, but because technology is changing fast they don't want to make any investment that requires more than three years to recover the firms initial investment. The cash flows for the three projects (A, B \& C) are listed below. a. Calculate the payback period of each project and indicate based on this calculation if the project should be accepted or rejected. b. Rank the 3 projects using their payback periods. Which project looks the best using this criterion