Answer
(a) $C(m)=129.50+0.15m$
(b) $258.50\ dollars$.
(c) $562\ miles$.
Work Step by Step
(a) Based on the given conditions, we can expresses the cost C as $C(m)=129.50+0.15m$
(b) Let $m=860\ miles$, we have$C(860)=129.50+0.15(860)=258.50\ dollars$.
(c) Let $C(m)=213.80$, we have $213.50=129.50+0.15m$, thus $m=\frac{213.50-129.50}{0.15}=562\ miles$.
