An article (A. Jennings, "What's Good for a Business Can Be Hard on Friends," The New York Times, August 4, 2007, pp. C1- C2) reported that according to a poll, the mean number of cell phone calls per month was 290 for 18-24-year-olds and 194 for 45-54-year-olds, whereas the mean number of text messages per month was 290 for 18-24-year-olds and 57 for 45-54-year-olds. Suppose that the poll was based on a sample of 100 18-24-year-olds and 100 45-54-year-olds and that the standard deviation of the number of cell phone calls per month was 100 for 18-24-year-olds and 90 for 45-54-year-olds, whereas the standard deviation of the number of text messages per month was 90 for 18-24-year-olds and 77 for 45-54-year-olds. Assume a level of significance of 0.05.

How do I construct and interpret a 95% confidence interval estimate for the difference in the mean number of cell phone calls per month for 18-24-year-olds and 45-54-year-olds.