Answer
no more than $80$ miles.
Work Step by Step
Step 1. Assume the customer can drive as far as $x$ miles per day. The cost for the second option is given by $cost2=24+0.2x$ dollars.
Step 2. Let $cost2\leq 40$. We have $24+0.2x\leq 40$ or $0.2x\leq16$ and $x\leq80$ miles.
