Answer: Choice B) [tex]7 \le r \le 12[/tex]
=============================================================
Explanation:
The domain is the set of allowed x inputs of a function.
How far to the left can we go on this red line? That would be x = 7.
How far to the right? That would be x = 12.
We can have x equal anything between 7 and 12, including both endpoints. We include the endpoints because they are filled in circles (as opposed to open holes).
So the domain is [tex]7 \le x \le 12[/tex]. If we replace x with r, then we update that inequality into [tex]7 \le r \le 12[/tex]. This replacement happens because r is along the horizontal x axis.
