The progenies of the dragons with strong fire and dragon with no fire will be dragons with fire at medium rate.
Step-by-step explanation:
Incomplete dominance is the phenomenon when two different alleles are present in a same organism gives a mixed type of phenotype which isn't similar to any characters of the parents.
In case of the dragons, the genotype of the dragons with strong fire = FF.
The genotype of the dragons with no fire = F'F'.
So the gametes produced by the dragon with strong fire is F and that by the dragons with no fire is F'.
So the dragons produced as a progeny = FF'.
As this gene shows incomplete dominance, so both the characters will be mixed and present as a mixed character. So the offsprings will be moderately fire breathing.