Okay, so this is basically our opponent square, for example number two. So we want to find the probability of two parents producing two children who are both female. And if we look at the pun and square, the only time we have both females, both girls is in this final square. And this gives us by the product rule. So this multiplied by this a value of one fourth. So essentially we take one half multiplied by one half because the probability of getting a girl the first time around is one half and the probability of getting a girl the second time around is also one half.