Answer:
White: A---
Black: aaB-
Brown: aabb
Explanation:
The given example represents dominant epistasis wherein the gene A masks the effect of gene B. Hence, all the genotypes having at least one copy of "A" allele will have white coat color (A---).
On the other hand, in absence of "A" allele, the "B" allele would be able to express itself. Hence, all the genotypes that have two copies of recessive "a" allele and atleast one "B" allele (aaB-) would have black coat color.
The brown coat color would be expressed in double homozygous recessive genotypes (aabb) only.
