In order to determine the miles per gallon rating for a new midsize minivan, an automaker wants to randomly select sample vehicles. The sample provided a sample mean of 31.56 mpg. The population standard deviation o is unknown. The sample standard deviation is .798. How large does the sample size have to be if we need to obtain a more precise, 95% interval with a margin of error of no more than .1? Use the sample standard deviation of .798 mpg as a planning standard deviation