In an article in Marketing Scionce, Silk and Berndt investigate the output of advertising agencies. They describe ad agency output by finding the shares of dolat biling volume coming from various media categories such as network television, spot television, newspapers, fadio. and so forth. (a) Suppose that a random sample of 396 U.S: advertising agencies pives an average percentage share of billing volume from network television equal to 7.45 percent, and assume that equals 1.49 percent. Caiculate a 95 percent confidence interval for the mean percentage share of billing volume from network television for the population of all U.S. advertising agencies. (Round your answers to 3 decimal places.) (b) Suppose that a random sample of 396 US. advertising agencies ghves an average percentage share of billing volume from spot television commercials equal to 12.49 percent, and assume that equa/s 1.55 percent. Calculate a 95 percent confidence interval for the mean percontage share of biling volume from spot television commercials for the population of all U.S. advenising agencies. (Round your answers to 3 decimal places.) (c) Compare the confidence intervals in parts a and b. Does it appen that the mean percentoge share of billing volume from spot television commercials for US: advertising agencies is greater than the mean percentage share of baling volume fiom network television? Explain