What is the ROC for this discrete signal:
HINT:

Remember that the ROC is the region in the $z$-plane for which the series

$$X(z)=\sum_{n=-\infty}^{\infty}x[n]z^{-n}\tag{1}$$

converges. Since you've found $X(z)$ you also know that $x[n]=4\delta[n-2]$, i.e. there's only one value of $n$ for which $x[n]$ is not equal to zero. What does that mean for the convergence of $(1)$?