I've been puzzled by this for some time now and would like to know the truth behind my madness

How do different skill bonuses that effect the same stat combine together?

For example I will use two skills:
Xion Particle Properties: +5% dmg to all ships per rank.
Offensive initiative: +2% dmg to destroyers and battle cruisers per rank.

So let's say we will use battlecruiser (Base ATK 18) and you have 1 point in each skill, how would the combination work?:

1. (2%+5%)*18= 19.26

Or

2. 18*2%*5%=19.278