Health Care Oregon wants to estimate the difference in the average number of sick days taken last year by two groups of employees, hourly workers and salaried employees. From the population of hourly workers you take a sample of 12 and find that the average number of sick days taken was 15.6. For a sample of 12 salaried employees, the average number of sick days taken was 11.2. The standard deviation turns out to be 1.8 days for both groups. Build a 95% confidence interval estimate of the difference in average sick days taken by the two populations represented here. (Assume the two population distributions are normal, with equal standard deviations.)