Given the information on the graph, we can see two points: (1,2) and (2,4), therefore, a quick analysis can give us the relation function as follows:
[tex]\begin{gathered} \text{slope:} \\ m=\frac{y_2-y_1}{x_2-x_1} \\ (x_1,y_1)=(1,2) \\ (x_2,y_2)=(2,4) \\ \Rightarrow m=\frac{4-2}{2-1}=\frac{2}{1}=2 \\ m=2 \\ y-y_1=m(x-x_1)_{} \\ \Rightarrow y-2=2(x-1)=2x-2 \\ \Rightarrow y=2x \end{gathered}[/tex]
as we can see, from the expression y=2x, the rental costs $2 per mile.
