Usually a company may charge a startup fee, is a charge for some things they need to do to start the service, in this case may just be paperwork, and it's $19.95, a fixed cost, and they're charging 17 cents or $0.17 for every mile driven, let's say that Molly is going to drive "m" miles, so the cost equation in "m" terms will be C(m) = 19.95 + 0.17m.
Now, we know she only has 40 bucks to spend, so, if she can keep her Cost to 40 bucks, how many miles can she go for?
[tex]C(m) = 19.95+0.17m\qquad \qquad \stackrel{\stackrel{cost}{\downarrow }}{40}=19.95+0.17m\implies 20.05=0.17m \\\\\\ \cfrac{20.05}{0.17}=m\implies 117.94\approx m[/tex]
now, if we were to round that up to whole miles, it'd be only 117.
