Please explain

Watch your cholesterol: A sample of 320 patients between the ages of 38 and 82 were given a combination of drugs ezetimibe and simvastatin. They achieved a mean reduction in total cholesterol of 0.95 millimole per liter. Assume the population standard deviation is o = 0.20. Part 1 of 3 (a) Construct a 98% confidence interval for the mean reduction in total cholesterol in patients who take this combination of drugs. Round the answer to at least two decimal places. A 98% confidence interval for the mean reduction in cholesterol is .92