Consider the multiple linear regression model for the baseball data that we constructed in Section 3.7.

a. Using this model predict the number of games won by a team that has an ERA of 3.8 and commits 78 errors.

b. Find a $95 % \mathrm{Cl}$ on the mean number of games won by the team from part a of this problem.

c. Use the simple linear regression model from Section 2.8 to predict the number of games won by a team that has an ERA of 3.8.

d. Find a $95 % \mathrm{Cl}$ on the mean number of games won by the team from part $\mathrm{c}$ of this problem.

e. Compare the two CIs from parts $b$ and $d$ of this problem. Has adding the second predictor (errors) improved the model's estimation capability?