How do you do this by hand, not through excel

What is the payback period on Popeye's purchase of a new pleasure boat for his tourist business? The expected cash flows appear below. (note: payback is in years; round to 2 decimals) Year O cash flow = -9,800,000 Year 1 cash flow = 3,100,000 Year 2 cash flow = 3,900,000 Year 3 cash flow = 2,300,000 Year 4 cash flow = 3,600,000 Year 5 cash flow = 2,300,000 Year 6 cash flow = 3,300,000