So sally is type B. The child is type O. So the child, the genotype has to be, oh, the only way to have the recessive phenotype is have two copies of the some chances to copies of the real. And the job must have got one from sally. Sally is the mother and you inherit one allele from each of your parents. That means sally's genotype has to be be bo B is dominant here. So she's blood type B. And she has an alibi that she was able to pass on to her child. Now how do you work out which of these blood types could not be the father. Let's do a punnett square. And in opponents square you have the gametes of the parents. Along the outside. So here are sally's gametes, but we don't know the fathers can meet. So I'm just going to put a question mark, question mark and we'll see what comes up. Okay. Oh even I'll put different color question marks because he he could have different styles. Okay, now I'm going to fill out this planet square. So this first column doesn't really matter because these are not going to be type. Okay, so this first column could be type B. Could be type A B. Depending on what the fathers alleles are. So let's just rule it out because it's not the child. The child is clearly from this column. It's one of these two squares. So what does your father need in order to have this type of a child? Well, he needs to have an aerial. So what blood types could have an org? You'll either of these? Well, it could be type O. Of course, because typo would just be this tina type. He could be type A. If he were visiting the time, he could be tight, big. If he were this genotype, any of these would have an O. A little that could be passed on to a child and he could be the father. However, imagine that he was type A B. Imagine that this was a B. So this one would be a. Oh, and this one would be beating. You can see that this pair could not have a typo child. This child will be type A and this child will be type B. So type A B is not a possibility, but it's the only one that isn't a possibility because any of these could provide an alien to the child. A B could not. So the answer here is only a B. So only A B. Is excluded