(Calculating inflation and project cash flows) On July 25, 2011, the average price of a gallon of gasoline was $3.20. Just 8 years later the price of that same gallon of gas was $2.23. What was the rate of inflation (deflation) in the price of a gallon of gas over the period? The annual rate of inflation (deflation) in the price of a gallon of gasoline over the 8 years was %. (Round to two decimal places.)