18.22 The state of Texas has reported the following quarterly gross sales for the in-state accommodation and food services industry for the years 2004-2008. Source: Texas Comptroller of Public Accounts site, ecpa.cpa.tx.us, August 22, 2009 Gross Sales ($ Billions) I II IV 2004 2005 2006 2007 2008 $7.014 7.441 8.166 8.642 9.412 7.330 7.904 8.390 9.322 9.879 7.260 7.716 8.321 9.136 9.578 7.521 8.228 8.751 9.599 9.995 a. Construct the four-quarter centered moving average for these data and determine the percentages of the moving average for the quarters. b. Determine the seasonal indexes for the quarters. Use the seasonal indexes to deseasonalize the original time series. c