Problem
You are in the market for a new car. A local dealership has a promotion for a new convertible; you pay no money today, but you must make annual payments of $15,000 at the end of each of the next 4 years. In looking at other dealerships, you know that you can purchase the same convertible for cash for $45,000 today (with no more payments in the future). What is the interest rate of the promotion that the dealer is advertising (as an EAR)?