So this is probably the hardest part to figure out, and we will, along the way, we'll actually probably figure out the top two terms. So what's the probability of B, or the probability of getting 4 out of 6 heads? Let's see what happens. Right when I put my hand into the bag and I pick out a coin, there's a 5 in 10 chance, or 5 in 15 chance, right, there are 15 total coins, that I pick a fair coin. So 5 in 15, that's the same thing as 1 third, that I pick a fair coin. And then there's a 2 thirds chance that I pick a unfair coin. Now if I pick a fair coin, given that I have a fair coin, what is the probability given the fair coin, what is the probability that I get 4 out of 6 heads?