The table lists the cost in millions of dollars for a 30-second commercial for selected years. a. Find a linear function f that models the data. Year 1993 1997 2004 2008 2011 Cost 18.8 19.4 20.3 20.8 21.2 b. Estimate the cost in 2009 and compare the estimate to the actual value of $21.2 million. Did your estimate involve interpolation or extrapolation? a. Use linear regression to determine the equation of the line that best fits the data. The linear function is f(x) = . (Type an expression using x as the variable. Use integers or decimals for any numbers in the expression. Round to three decimal places as needed.)