U.S. postal rates have steadily increased since 1932. Using data depicted in the table in the next column for the years 1971–2020, the cost in cents to mail a single letter can be modeled using a quadratic formula as follows: 

C(t) = -0.00246t² + 1.02t + 7.44 

where t is the number of years since 1970.

(a) Find the predicted cost of mailing a letter in 1995 and 2015 and compare these estimates with the actual rates.
(b) Find the rate of change of the postage cost for the years 1995 and 2015 and interpret your results.
(c) Using the regression feature on a graphing calculator, find a cubic function that models these data, letting t = 0 correspond to the year 1970. Then use your answer to find the rate of change of the postage cost for the years 1995 and 2015.

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Year 1971 1974 1975 1978 1981 1981 1985 1988 1991 1995 1999 2001 Cost 8 10 13 15 18 20 22 25 29 32 33 34 Year 2002 2006 2007 2008 2009 2012 2013 2014 2016 2017 2018 2019 Cost 37 39 41 42 44 45 46 49 47 49 50 55