Explanation:
to be a function every value of x must have exactly one value of y.
in other words, if you create a vertical line and move it across the whole chart (e.g. from left to right), this line must not even once intersect the function curve more or less than once.
so, this is clearly a given here. yes, it is a function.
the domain is the interval or set of all valid x (input) values. and that starts on the right with x = 5 (included in the function indicated by the filled dot). and it goes endlessly to the left. that means -infinity (but not included as "infinity" is only a symbol but not a number).
-infinity < x <= 5
the range is the interval or set of all valid y (function result) values.
and that starts on the top with y = 2 (included). and it goes endlessly down. that means again -infinity (not included).
-infinity < y <= 2