The travel-to-work time for residents of the 15 largest cities in the United States is reported in the2003 Information Please Almanac.Suppose that a preliminary simple random sample of residents of San Francisco is used to develop a planning value of 6.41 minutes for the population standard deviation.

a.If we want to estimate the population mean travel-to-work time for San Francisco residents with a margin of error of 4 minutes, what sample size should be used? Assume 95% confidence.

b.If we want to estimate the population mean travel-to-work time for San Francisco residents with a margin of error of 3 minutes, what sample size should be used? Assume 95% confidence.