2.67 Fuel consumption for different types of vehicles. In Exercise 2.23 (page 97), you examined the relationship between CO₂ emissions and highway fuel consumption for 1067 vehicles. You used different plotting symbols for the four different types of fuel used by these vehicles: regular, premium, diesel, and ethanol.

1. (a) Find the least-squares equation for predicting CO₂ emissions from highway fuel consumption for all 1067 vehicles.

2. (b) Make a scatterplot of the data with the fitted line.

3. (c) Based on what you learned from Example 2.23, do you think that a single least-squares regression line provides a good fit for all four types of vehicles? Explain your answer.