Can someone clarify base AD ratios on Mega Gnar?

Just a quick question, and I know it is listed on the wiki although the way it is listed is a bit confusing. What are the ratios per lvl (1-18) for both mini gnar and mega gnar for base AD?

Also, does sterak's gage stack like this: Base AD of 100 --> 4 steraks gage's --> New AD of 200 (accumulative) or cumulatively, so a 25% increase, then another 25% increase of that, and so on.

Thank you