Random and independent samples of 55 recent prime time airings from each of two major networks have been considered. The first network aired a mean of commercials during prime time, with a standard deviation of commercials. The second network aired a mean of commercials, with a standard deviation of commercials. As the sample sizes are quite large, the population standard deviations can be estimated using the sample standard deviations. Construct a confidence interval for , the difference between the mean number of commercials aired during prime time by the first network and the mean number of commercials aired during prime time by the second network. Then find the lower limit and upper limit of the confidence interval.