Zachary's maximum expenditure is $82/day. The fixed, base cost of the rental is $40, so subtracting $40 from $82, we are left with $42 per day that Zachary can spend on mileage. Dividing $42 by $0.21, we are left with a value of 200; thus he can drive the car 200 miles per day without exceeding his rental allowance.
