Using the Body Fat data set with training set bodyfat-tr.xlsx and validation set bodyfat-val.xlsx

(a) fit a simple linear regression model relating percent body fat (PCTBF) to wrist circumference (Wrist) on the training set.

(b) predict the values of PCTBF using the fitted model on the validation set.

(c) determine whether or not the fitted model based on the training set is validated with the validation set.