Customers arrive at a move theater ot the advertised movie time only to find that they have to sit through several previews and prepreview ads before the movie starts of time devoted to previews was 4 minutes. Use that as a planhing value for the standard deviation in answering the following questions. Round your animer to next whole number. a. If we want to estimate the population mean time for previews at move theaters with a margin of error of 75 seconds, what sample supe should be used? Atifume 95% conlidence, b. If we want to estamate the populabon mean time for previews at move theoters wath a margin of error of 1 minute, what sample size shouid be used? Assume 95% contidence