#### Answer

$\text{
a function
}\\\text{Domain: all real numbers}
\\\text{Range: }
(-\infty,4]$

#### Work Step by Step

$\bf{\text{Solution Outline:}}$
To determine if the given graph is a function, use the Vertical Line Test.
$\bf{\text{Solution Details:}}$
A vertical line drawn anywhere will intersect the given graph in only $1$ point. By the Vertical Line Test, the given is a function.
The domain is the set of all $x$-values, while the range is the set of all $y$-values. Hence, the given set of points has the following characteristics:
\begin{array}{l}\require{cancel}
\text{
a function
}\\\text{Domain: all real numbers}
\\\text{Range: }
(-\infty,4]
.\end{array}