Well from the the information, you gather that small wings are recessive traits, and white wings are recessive traits. To exhibit a recessive trait, you need homozygous (the same) alleles of the trait, else it won't show through
So because the two butterflies are exhibiting these traits, the only alleles they have are for small wings and white wings, so the only alleles they can give on to their offspring are ones for small, white wings, so the chance is 100%
