Stella's equation is given by
![y=(0.5)/(40)x+100](https://img.qammunity.org/2023/formulas/mathematics/college/5zlfk5jlvg320b1m51fx0c02dffxa47bsx.png)
where x represents the miles, y the total cost and 100 is the flat rate.
Now, since the maximun amount of money is $270, we need to find x in our formula. that is,
![270=(0.5)/(40)x+100](https://img.qammunity.org/2023/formulas/mathematics/college/r3cx71vt5w99fxdj6x6ik863eqcj8z4jrt.png)
Then, by moving 100 to the left hand side, we get
![\begin{gathered} 270-100=0.5x \\ 170=0.5x \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/uzq22a0h9du818tcf7ll773ooexn685pjg.png)
then x is given by
![\begin{gathered} x=(170)/(0.5) \\ x=340 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/1y5htgq8ty04dsiiee4tsskywkv8ofbzui.png)
so, the greatest number of miles is 340 miles