Answer
$400$ miles
Work Step by Step
Total cost of renting the truck is:
$C=65*d+0.20*m$, where $d$=days rented and $m$=miles driven.
For Michael, the cost is \$275 for 3 days:
$275=65*3+0.2*m$
We solve for $m$:
$m=(275-65*3)/0.2=80/0.2=400$ miles
