let take two points as miles and gas used:
[tex]\begin{gathered} (x_1,y_1)=(3,228) \\ (x_2,y_2)=(5,380) \end{gathered}[/tex]First find the slope:
[tex]\begin{gathered} m=\frac{y_2-y_1}{x_2-x_1} \\ m=\frac{380-228}{5-3} \\ m=\frac{152}{2} \\ m=76 \end{gathered}[/tex]Now find the equation at initial condition where distance and gas used are equal to zero.
[tex]\begin{gathered} (y-y_0)=m(x-x_0) \\ y-0=76(x-0) \\ y=76x \end{gathered}[/tex]