Cystic fibrosis is a recessive allele, meaning that the child must be aa to suffer the symptoms. Only 1/4 of the paired alleles is aa, so the probability of getting cystic fibrosis would be 25%.
75% is the chance because a capital letter means it’s a dominant allele meaning it’s a possible outcome there’s 3 capital letter for which it’s 75 since each box is worth 25
