Blood type prediction help?

Ok, a man who is heterozygous for type A means that he is AO, because for type A blood you can only be zygous which is AA and heterozygous which is AO; and he marries a woman who is AB. You first have to make a 4 square punnett square layout. After you make the punnet square you place AO on the left side and AB on the top and you combine the letters. In the first box you get AA, second box on the right you get AB, the bottom left box you get AO and the last box on the right you get BO. So, you are asked what is the probability that the child will be type B blood and the possibilities for type B blood is zygous BB and heterozygous BO. When you look in the punnett square, you will find out that BO is in the fourth column which is �; which is converted to 0.25%. So you have a 0.25% chance of having a child which is type B blood.