If one parent has Type A blood and the other has type B, but all four types are represented among the offspring, what are the genotypes of the parents? If both parents are blood type A but ¾ of their children are type A and ¼ of the children are type O, what are the parent's genotypes?

What genotypes must the parents be if one has type AB blood and the other has type B, but their children are ¼ A, ¼ AB and ½ type B?