Your budget = $66.
Car rental (for the car) = $45
Car rental (for each mile) = $0.21.
To work out the price you can afford, do 66 - 45 = $21.
Now do $21 ÷ $0.21 to find out the number of miles you can drive.
$21 ÷ $0.21 = 100 miles.
You can drive for 100 miles.