The average rate of change is 1
2-1=1
3-2=1
4-3=1
<span>A value is in the domain if there is a point on the graph of the function at that x-value</span>
The domain is

and the range is

Domain is x values (horizontal axis), while range is y values (vertical axis). On a line like this one, domain is calculated from the left most point to the right most, while range is calculated from the down most to the upmost.
Because this line is a solid line rather than a dotted line, less than or equal to

signs are used rather than just

less than signs.
If the questions are asking where the two equations meet the answer is (1,1)