U.S. cellular phone subscribership has been reported as shown here for the 1996€“2007 period.

a. Fit a linear trend equation to the time series. Using this equation, determine the trend estimate for 2013.
b. Fit a quadratic equation to the time series, then use the equation to determine the trend estimate for 2013.
c. Construct a graph of the time series along with the equations fitted in parts (a) and (b). Which equation appears to better fit the data?

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Subscribers (Millions) 44.0 55.3 69.2 86.0 109.5 128.4 Subscribers (Millions) 140.8 158.7 182.1 207.9 233.0 255.4 5 Year 1996 1997 1998 1999 2000 2001 Year 2002 2003 2004 2005 2006 2007 2