By using data from the U.S. Bureau of Labor Statistics for the years 1968-2008, the purchasing power P of a 1983 dollar can be modeled by the function
P(t) = 3.443(1.046)-t
where t is the number of years past 1960.
Use the model to find the function that models the rate of change of the purchasing power of the 1983 dollar and use that function to predict the rate of change in the year 2015.