So what exactly do we mean by at most two boys? Well, what this means is we actually have to look at three different cases. So at most means we can have no boys or we can have one boy or we can have two boys, but we cannot have three boys because we want at most two boys. So basically we have to look at three individual cases when we have zero boys, when we have one boy, and when we have two boys, okay? And then we find the probabilities of these events and we sum them up because they are mutually exclusive. So let's begin with zero boys.