How do they work?

I get that they add a percentage of X stat, but when they get removed, HOW is it calculated? Do they take the stat and subtract X% from it? Or do they just redo the math excluding the buff? Because I've been looking at my Kage Minato, doing the math on his attack for 9 tails at the end of round 4. Asuma's is one of the 3 (Tobirama and Wind main's being the other), but I know that kage's gonna get the 9% scaling, so I accounted this. But I'm just wondering, mainly out of pure curiosity, does it subtract X% or redo the math without said buff, but with all others?

If that makes sense

Edit-Also, regarding buffs. How do they stack? Do they add on the percentage? Like they add on lets say....

Wind's 40%, then Tobirama's 30%, then Asuma's 30%? Do they add the percentages based off the new value? Or add them onto the new value based off of the original?

(Example, Minato has 10k attack (Mine actually has 10385, but still, for example), he gets 40% from wind. 14000 now., when Tobirama's is added, does it...

A-Add on 4200 (30% of 14000)

or B-Add on 3000 (30% of the original)