Two growth hormones are being considered. a random sample of 10 rats was given the first hormone and their average weight gain was 2.3 pounds with standard deviation of .4 pounds. for the second hormone, a random sample of 15 rats had an average weight gain of 1.9 pounds with standard deviation .2 pounds. assume the weight gains follow a normal distribution. find a 90% confidence interval for the difference in average weight gain for the two growth hormones.