Hi! Any help on this statistics question about confidence interval estimates would be greatly appreciated.

A clinical trial was conducted to test the effectiveness of a drug used for treating insomnia in older subjects. After treatment with the drug, 19 subjects had a mean wake time of 97.2 min and a standard deviation of 40.7 min. Assume that the 19 sample values appear to be from a normally distributed population and construct a 98% confidence interval estimate of the standard deviation of the wake times for a population with the drug treatments. Does the result indicate whether the treatment is effective? Find the confidence interval estimate. min