Revenue passenger-miles are calculated by multiplying the number of paying passengers by the distance flow n in thousands. The accompanying table shows a portion of monthly data on revenue passenger miles (in millions) from January 2006 through September 2010; the full data set can be found on the text website, labeled Revenue Passenger-Miles.

a. Plot the above series and comment on its trend and seasonal variations.

b. Compute seasonal indices and use them to seasonally adjust the series.

c. Fit the appropriate trend model to the seasonally adjusted series.

d. Use decomposition analysis to make monthly forecasts for the last three months of 2010.