In a book named Treasure, the reader has to figure out where a 2.2 pound, 24 kt gold horse has been buried. If the horse is found, a prize of $24,500 a year for 20 years is provided. The actual cost to the publisher to purchase an annuity to pay for the prize is $224,000. What interest rate (to the nearest percent) was used to determine the amount of the annuity? (Assume end-of-year payments.)