Answer:
3
Explanation:
Heterozygous mice at both loci would be BbAa genotype.
B (black) is dominant over b (white) but the presence of A results in agouti.
Crossing two heterozygous:
   BbAa   x   BbAa
Progeny
9 B_A_ - Agouti
3 bbA_ - agouti
3 B_aa - Black
1 bbaa - white
Hence, 3 out of 16 progeny will be black in color.
See the attached image for the Punnet's square analysis of the cross.