The data in the data frame asset are from Myers (1990), \Classical and Modern Regression with Applications (Second Edition)," Duxbury. The response y here is rm return on assets for thirty companies in 1982. We wish to predict the response in terms of the predictors x1-x7. Fit a linear model including all the predictors. Use the drop1 command to rank models obtained from the original model by deleting one predictor variable. If the model can be improved by deletion of a variable, t the reduced model. Iterate this procedure of examining one variable deletions until the model can no longer be improved (according to AIC) by any one variable deletion. For the nal model, plot diagnostic quantities and comment on these plots.