An environmentalist would like to compare air pollution levels in cities A and B. From each city 10 measurements are taken. For city A, the average of all measurements (where measurements are percentage of pollutants in the air) is 5 percent with sample standard deviation 1.5 percent. For city B the average of all 10 measurements is 5.4 percent with sample standard deviation 2 percent. Assume that for each city air pollution level at a random time and location follows a normal distribution, and nd a 90% confidence interval for difference between the true average air pollution levels of city A and city B.