So this equals 15 times 1 half to the 6th. What's 1 half to the 6th? That's 1 over 64, right? 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.