A clinical trial was conducted to test the effectiveness of a drug use for treating insomnia in older subjects. after treatment with the drug 20 subjects had a mean wake time of 94.2 minutes and a standard deviation of 41.9 minutes. assume that the 20 sample values appear to be from a normally distributed population and construct a 95% confidence interval estimate of the standard deviation of the week times for a population with the drug treatments. Find the confidence interval estimate