suppose that cars with six-cylinder engines have mpg that is normally distributed with mean 22 and standard deviation 1.2, while cars with four-cylinders have mpg normally distributed with mean 26 and standard deviation 1.5. two cars with six-cylinder engines and three with four-cylinder engines are to be driven over a 300-mile course. let x1,...,x5 denote the resulting fuel efficiencies (mpg). assume that cars are randomly sampled from their populations. consider the linear combination