So 1 over 64, so it becomes 15 over 64. So the probability of getting 4 out of 6 heads, given a fair coin, is 15 out of 64. So this is the probability of 4 out of 6 heads, given a fair coin. And if you look at it, based on our definition of B and A, this is the probability of B given A. B is 4 out of 6 heads, given a fair coin. Fair enough. So let's figure out the probability of, because there's two ways of getting 4 out of 6 heads.