Question about Slayer studied target

[Thormind]

Studied target gives a bonus on dmg rolls. I am not sure how that bonus is applied.

As an example if the base dmg from my sword is 1d6 and i do 3d6 sneak dmg. Lets say i do not have any other dmg bonus than a +3 from studied target. On one sneak attack, is the dmg calculated like:

a: (1d6+3)+(3d6+9) - applied on all dice rolls
b: (1d6+3)+(3d6+3) - applied once on sword dmg and once on sneak dmg
c: (1d6+3d6)+3 - applied only once per attack

Thanks!

[blahpers]

C. Like any other bonus to an attack's damage, it applies only once per attack.