4. Suppose that the continuous random variables (X, Y, Z) have a valid joint probability density function
$f(x, y, z) = Kxyz^2, \quad 0 \le x, y \le 1, \quad 0 \le z \le 3.$
Then, E(Y) = 　(4) 　 and $E(Y|X = \frac{1}{2}, Z = 1) =$ 　(5) 　. Of course, you should find the value of K first.