A: Gansk has set the precedent that one cannot tell how much an invisible opponent has been affected by a breath weapon.
Vorel hits all six times, once with a wing to the franistan (worst roll 42+2+2-4=42) for a total of 110+10+24=144 points of damage. Dreargak has 207 HP remaining.
Dreargak hits with a claw to the franistan, but with nothing else, (rolled 54-5=49 to confirm crit; best missing roll 51-4=47) for 32 points of damage. Vorel has 370 HP remaining.
Vorel misses with a wing, but to make up for it bites Dreargak in the franistan (best missing roll 39+2+2-6=37; worst hitting roll 43+2+2-6=41) for a total of 114+10+36=160 points of damage. Dreargak has 47 HP remaining.