The combined cityfhighway fuel economy of a 2016 Toyota 4Runner 2WD 6 cylinder 4L automatic 5speed using regular gas is a normally distributed random variable with a range 1? mpg to 22 mpg. (a) Estimate the standard deviation using Method 3 (the Empirical Rule for a normal distribution) from Table 8.8. (Round your answer to 4 decimal places.) Standard deviation I I (b) What sample size is needed to estimate the mean with 90 percent condence and an error of :r 0.25 mpg? (Enter your answer as a whole number. Use a z-value taken to three decimal places in your calculations.) Sample size