Damage bonus stacking question.

If I had a bow with a 15>50 bonus, a 20% vs something mod and it was customised for me giving it another 20% damage on top, how would this add up?
If I met all the conditions - my health is above 50%, I'm attacking whatever gives me the bonus for the Vs mod, would I get 55% extra damage or do the bonuses stack in a different way?

No they stack like you said. 55% extra damage, not bad

if you have a shock weapon and have "air attunement" - when does the + damage (I think its 1-17) get added , before you add +55% or after you add +55% ?

I believe but not positive that the damages there are seperate... U would do your dmg +55% dmg then your 1-17 as well. Could be wrong but pretty sure.

Percentages multiply when they are "stacked." So you get: 1.15 x 1.2 x 1.2 = 1.656, or 1.66. So you get +66% damage from that weapon whenever you fight the enemies it provides a bonus for.