The U.S. dollar has been declining in value over the last century, except during the Great Depression, when it increased in value. The following table shows the number of dollars it took in various years to equal $1 in 1913.

(a) Using the regression feature on a graphing calculator, find a cubic function that models these data, letting t = 0 correspond to the year 1900.
(b) Using your answer to part (a), find and interpret the rate that the number of dollars required to equal $1 in 1913 was increasing in 1955 and 2015.

Year 1913 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 2020 Number of Dollars It Took to Equal $1 in 1913 1.00 2.02 1.69 1.41 2.53 2.99 3.92 8.32 13.20 17.39 22.02 26.32