stuck on these, pls help :)

Customers arrive at a movie theater at the advertised movie time only to find that they have to sit through several previews and prepreview ads before the movie starts. Many complain that the time devoted to previews is too long. A preliminary sample conducted by The Wall Street Journal showed that the standard deviation of the amount of time devoted to previews was four minutes. Use that as a planning value for the standard deviation in answering the foliowing questions. a. If we want to estimate the population mean time for previews at movie theaters with a margin of error of 69 seconds, what sample size should be used? Assume 95% confidence. b. If we want to estimate the population mean time for previews at movie theaters with a margin of error of I minute, what sample size should be used? Assume 95% confidence. Health insurers are beginning to offer telemedicine services online that replace the common office visit. Wellpoint provides a video service that aliows subscribers to connect with a physician online and receive prescribed treatments. Wellpoint claims that users of its LiveHealth Online service saved a significa amount of money on a typical visit. The data shown below (5), for a sample of 20 online doctor visits, are consistent with the savings per visit reported by Wellpoint. Assuming the population is roughly symmetric, construct a 95% confidence interval for the mean savings for a televisit to the doctor as opposed to an office visit (to 2 decimals). 95% confidence interval: 7