So let's figure out the probability of, because there's two ways of getting 4 out of 6 heads. One, that we picked a fair coin, and then times 15 out of 64, and then there's a probability that we picked an unfair coin. So what's the probability of the unfair coin? Of getting 4 out of 6 heads, given the unfair coin? Well, once again, what's the probability of each of the combinations where you get 4 out of 6? So in this situation, let's do the same one. Heads, tails, heads, tails, heads, heads.