Consider the bearing wear data and multiple linear regression model in Exercise 6-17.

(a) Find the mean bearing wear given that the oil viscosity is 25.0 and the load is 1100.

(b) Compute a 99% CI on this mean response.

(c) Compute a 99% PI on a future observation when the oil viscosity is 25.0 and the load is 1100.

(d) What do you notice about the relative size of these two intervals?

Which is wider and why?