As a resident of New York City, you are considering purchasing a new Toyota Prius. The Prius sells for $20,000. Your annual expense of owning and driving the car is $3,000 (most of which is the cost of parking the car in a Manhattan garage). If you do not purchase the car, you will spend $5,000 per year on public transportation and rental cars. The interest rate is 4%. What is the smallest number of years that you must own the car so that the discounted cost of owning the car is less than the discounted cost of the alternative?