Like it says on the tin. Let's say a fire dragon wyrmling is directly in front of a wall of water – wall is less then a square away – and on the other side is its target. The target is 15 feet away, but again, directly in front of the dragon is a wall of water, which as per spell instructions is 30 feet long, 10 feet high, and 1 foot thick. Both targets are on the ground, and looking at the center of the water wall, but on opposite sides. The Red Dragon Wyrmling breathes in a 15 foot cone, which would have to go through the wall entirely to hit the target. Would the fire breath work?