So let's just think about how do we calculate, how would we calculate a mean if we knew what question mark is? Well, we would take the total, we would take the total of ages, of ages, we would then divide that by the number of children, we would then divide that by the number of ages that we had, and then that would be equal to, that would be equal to the mean. Or another way to think about it, if you multiply both sides times the number of ages, the number of ages on that side and the number of, of ages on that side, then this is going to cancel with that, and we're going to be left with the total, the total is going to be equal to, is going to be equal to the mean times the number of ages. Mean times, and I'll just write times the number, times number of data points, or number of ages. So maybe we can use this information, because we're just going to have this missing question mark here, and we know the mean and we know the number of ages, so we just have to solve for the question mark, so let's do that. So let's go back to the beginning here, just so that this makes sense with some numbers. The total of ages, that's going to be five plus two plus question mark, plus question mark, plus two, this two, plus two, plus four, plus eight.