What's the formula for stacking buffs anyway? Let's say we have a Minato attacking while under the effects of Iruka's Passive (30%), a barrier (40%) and a WM's passive (40%). Is the net increase 30+40+40=110% or 1.3*1.4*1.4=2.548 (154.8%)?

EDIT: I did some minor testing with a pretty small sample size, but it looks like the buffs are additive (i.e. 30+40+40). Confirm/debunk pls?