Answer
See graph.
Domain: $\{3\}$
Range: $(-\infty,\infty)$
Work Step by Step
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: $(-\infty,\infty)$