U.S. cellular phone subscribership has been reported as shown below for the 1993€“2004 period.

a. Fit a linear trend equation to the time series. Using this equation, determine the trend estimate for 2010.
b. Fit a quadratic equation to the time series, then use the equation to determine the trend estimate for 2010.
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 Subscribers (Millions) (Millions) Year Year 1993 86.0 16.0 1999 1994 24.1 2000 109.5 2001 1995 33.8 128.4 1996 44.0 2002 140.8 1997 55.3 2003 158.7 1998 69.2 2004 182.1