Please explain the discount part. I don't know how to do it.

The management of Bar-None Manufacturing Co. is considering three investment projects for the next year but doesn'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 are found below. - According to the payback method, which of the projects qualify for acceptance? - If Bar-None uses a 10% discount rate to analyze projects, what is the discounted payback period for each of the three projects? And which project should the firm undertake