Continuing the previous problem, the files P18_10 1987.txt through P18_10 1990.txt contain data on Barry Bonds's at-bats during each of the four seasons 1987-1990. The file P18_10 Variables.txt lists the variables in each file. Import each year's data into Excel. Then bring all of the data into a single Excel (.xlsx) file with four sheets, one for each year. Enter variable names in the top row of each sheet (you can use the ones suggested in the P18_10 Variables.txt file), and replace all missing values with blanks. (They are currently denoted by periods.) Finally, for any year of your choice, create a pivot table that allows you to see how Bonds's batting success varied by possible explanatory variables. For example, did he have more success in home games than away games?