For each data table, before answering the questions, determine whether the simple regression model is a reasonable description of the association between the two indicated variables. In particular, consider the conditions needed for the reliable use of the SRM. Then answer the listed questions. The data tables for these exercises are the same as those used for the like-numbered exercises in Chapter 19.

The cases that make up this data set are types of cars. The data include the engine size or displacement (in liters) and horsepower (HP) of 311 vehicles sold in the United States in 2016. Use the SRM of the horsepower on the engine displacement to answer these questions.

(a) A manufacturer offers 3- and 3.5-liter engines in a particular model car. Based on these data, how much more horsepower should one expect the larger engine to produce? Give your answer as a 95% confidence interval.

(b) Do you have any qualms about presenting this interval as an appropriate 95% range?

(c) Based on the fit of this regression model, what is the expected horsepower of a car with a 3.5-liter engine? Give your answer as a 95% prediction interval. Do you think that usual prediction interval is reasonable? Explain.