Use R.

1 Problem 1 In the dataset "infectionrisk.txt", we are interested in the effect of average length of stay in the hospital (Stay) and number of X-rays (Xray) on the infection risk (InfctRsk). 1. Fit a multiple linear regression model based on the three variables and report the regression equation. 2. Are the residuals approximately normally distributed? Create a QQ plot. 3. Does the linearity assumption hold? Create partial residual plots for the two predictors. 4. Add a quadratic term of the predictor variable Stay in the above model. Report the new quadratic regression equation. 5. Create partial residual plots for the newly fitted quadratic regression model. What are the differences compared with the ones in subquestion 3?