Calculating ROI for startup

Hi,

I have been watching videos on youtube and researching everything I can find on what the correct way is to calculate return on investment to get investors on board for a startup company. I have The below format outlines what I am trying to do with investment options and % profit and payback period what I am stuck with is not knowing the formula to help calculate the payback amount.

Beneath each figure I have populated a %growth (if one applies) to demonstrate the revenue uplift.

I have attached the table below of what I am trying to achieve

Any assistance offered is really beneficial to someone clearly struggling!