10. Mendel's Principle of Independent Assortment gives the 9:3:3:1 phenotypic ratio for a dihybrid cross [create a Punnett square if necessary - the gametes will be HB, hB, Hb, hb].
11. If the parents are HHBB and hhbb, all of the F1 generation will be HhBb, so they will all have long, black hair, as H > h and B > b (100%).
12. Assuming the genes assort independently, we can do this by probability instead of filling in a Punnett square. In a cross between Hh x hh, 1/2 of the offspring will have short hair (hh). In a cross between Bb x bb, 1/2 of the offspring will have black hair (Bb). (1/2) x (1/2) = 1/4 of the offspring of the cross will have the short, black hair phenotypes [with the genotype hhB-].