How to determine the payback period?

Before looking at the workbook Tennis Option Analysis.xlsx, look at the problem below:

In cells B29:C29, enter the payback period (year number) for each option. (Optional Challenge: Write the necessary formulas to automatically calculate the year number in which the cumulative total income exceeds $0.)

For the optional challenge: How do I do this?

You can edit my workbook and resubmit it if you want to.