Two unlinked loci affect mouse hair colour. At one locus, the 'B' allele (agouti coat) is dominant to the 'b' allele (black coat).

Two unlinked loci affect mouse hair colour. At one locus, the 'B' allele (agouti coat) is dominant to the 'b' allele (black coat). At the second locus, the 'a' allele can act to block expression from the 'B/b' locus to express albinism. Mice with genotype 'aa' are albino because all the pigment produced at the 'B/b' locus is blocked. What would the phenotype ratio be for the result of a cross between two agouti mice with the genotype AaBb? 

a. 8 agouti: 4 black : 4 albino 

b. 9 agouti: 3 black : 4 albino 

c. 3 agouti : 9 black : 4 albino 

d. 4 agouti : 8 black : 4 albino 

e. 9 agouti: 4 black : 3 albino 

Please explain steps to figuring this out