Explanation:
the domain of a function is the interval or set of all valid x (input) values.
the range of a function is the interval or set of all valid y (function result) values.
the graph shows us that the x values are continuously between -5 and +3.
and the end points are filled, so, they are to be included as valid points (via the <= or >= signs).
so, the domain is
-5 <= x <= 3