so... for one day and no miles, the car costs 30*1, for 2 days 30*2, for 30*3 and so on, for "d" days, the car costs 30*d or 30d
now, if the driver drives it for 1 mile, the mileage costs is 0.20*1, for 2 miles is 0.20*2 for 3 miles is 0.20*3 and so on, for "m" miles, it costs 0.20*m or 0.2m
so, the actual costs to rent the car "d" days for "m" miles is really
C( d, m ) = 30d+0.20m
so.. if someone had only $250 to spend, and needs it for 60miles each day, how many days is that? [tex]\bf C( d, m ) = 30d+0.20m\qquad
\begin{cases}
C(d,m)=250\\
m=60
\end{cases}\\\\\\ 250=30d+0.20(60)[/tex]
solve for "d"
