1. The joint pmf of two random variables X and Y is given by
$$P_{X,Y}(x,y) = \begin{cases}
c(x+y) & x = 1,2; y = 1,2,3 \\
0 & \text{elsewhere}
\end{cases}$$
(a) Find the constant c.
(b) Find the marginal pmf of X and of Y.
(c) Find the probability P[Y > X].