Answer:
75% (3:4)
Explanation:
A hybrid organism is one that is heterozygous - it carries one curled allele and one normal allele.
Let's use the letter C. The curled allele is C, the normal allele is c.
The heterozygotes are therefore Cc.
The cross between the two cats is Cc x Cc.
C c
C CC Cc
c Cc cc
Organisms with the genotype CC and Cc are curled ears, since the C allele is dominant to the c allele.
1:4 of the genotypes are CC, and 1:2 are Cc, so 3:4 (75%) have the curled ear phenotype.