(a) Using thestacklossdata, t a model withstack.lossas the response and the other three variables as predictors using the following methods:

1.Least squares 2.Least absolute deviations 3.Huber's robust regression 4.Least trimmed squares. Compare the results.

(b) Now use diagnostic methods to detect any outliers or inuential points. Remove these points and then use least squares. Compare the results with part (a), and the other robust regression results.