Compound Poisson Sum: Mean and Variance via Eve's Law

Let $N \sim \operatorname{Poisson}(4)$ and, given $N$, let $X_1, \ldots, X_N$ be i.i.d.\ with $E[X_i] = 3$ and $\operatorname{Var}(X_i) = 2$. Set $S = X_1 + \cdots + X_N$ (with $S = 0$ when $N = 0$). Using the tower property and Eve's law, find $E[S]$ and $\operatorname{Var}(S)$.