by Razoupaf
You will do:3 damage, for casting Eternal Ember (0 base, +1 for breach IV, +1 for Fulminate, times 2).
4 damage, then 4 damage, for casting Double Tap (1 base, +1 1 for breach III, +1 for Fulminate, times 2).
You have 3 instances of damage. You can deal damage to up to three targets.
Edit: that's for casting Eternal Ember only, of course. When casting Double Tap on its own you'll do
4 damage, then 4 damage, for casting Double Tap (1 base, +1 1 for breach III, +1 for Fulminate, times 2).
on top.