Answer
See graph.
Domain: $\{-3\}$
Range: $(-\infty,\infty)$
Work Step by Step
First we solve $3+x=0$:
$3+x=0$
$x=-3$
We graph $x=-3$ by recognizing that it represents a vertical line through the point $(-3,0)$. See graph for result.
Since the graph is a vertical line, we know that the domain is restricted to $-3$, while the range is all real numbers:
Domain: $\{-3\}$
Range: $(-\infty,\infty)$