Consider the power consumption data and multiple linear regression model in Exercise 6-21.

(a) Find the mean power consumption given that x1  75F, x2  24 days, x3  90%, and x4  98 tons.

(b) Compute a 95% CI on this mean response.

(c) Compute a 95% PI on a future observation when x1  75F, x2  24 days, x3  90%, and x4  98 tons.

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

Which is wider and why?