Tires placed on the rear of your car will wear out after 21000 miles, while tires on the front
of your car will last for 29000 miles.
Suppose you have a new car and five identical new tires (four installed and one spare).
a) What is the maximum distance you can drive, assuming you can easily change the tires any time you want?
b) Describe a rotation schedule that allows you to drive this distance.