2. The joint probability mass function of the random variables X, Y, Z is

$$p(1, 2, 3) = p(2, 1, 1) = p(2, 2, 1) = p(2, 3, 2) = \frac{1}{4}$$, Find

(a) E[XYZ], and

(b) E[XY + XZ + YZ].