Data from the EPA’s Fuel Efficiency Guide suggests an approximate linear relationship between y = highway fuel efficiency (mpg) and x = weight (lbs) for midsize cars. Suppose the equation of the true regression line is ƒ(x) = 70 − .0085x.

a. What is the expected value of highway fuel efficiency when weight = 2500 lbs?
b. By how much can we expect highway fuel efficiency to change when weight increases by 1 lb?
c. Answer part (b) for an increase of 500 lbs.
d. Answer part (b) for a decrease of 500 lbs.