The U. S. Department of Energy's Fuel Economy Guide provides fuel efficiency data for cars and trucks. A portion of the data for 311 compact, midsized, and large cars follows. The Class column identifies the size of the car: Compact, Midsize, or Large. The Displacement column shows the engine's displacement in liters. The Fuel Type column shows whether the car uses premium (P) or regular (R) fuel, and the Hwy MPG column shows the fuel efficiency rating for highway driving in terms of miles per gallon. The complete data set is contained in the file FuelData. (Let x1 represent the engine's displacement, x2 represent ClassMidsize, x3 represent ClassLarge, x4 represent FuelPremium, and y represent HwyMPG.) (a) Develop an estimated regression equation that can be used to predict the fuel efficiency for highway driving given the engine's displacement. (Round your numerical values to four decimal places.)