Owners of cars kept track of their average fuel economy for a month. The results are shown below. At 90 percent confidence, how large a sample would provide a margin of error 2.5? (Use the planning...

Owners of cars kept track of their average fuel economy for a month. The results are shown below. At 90 percent confidence, how large a sample would provide a margin of error 2.5? (Use the planning value for the population standard deviation)