The following measurements (in picocuries per liter) were recorded by a set of argon gas detectors installed in a waste disposal facility: 569.5,549.2,524.9,538.3 Using these measurements, construct a 95% confidence interval for the mean level of argon gas present in the facility. Assume the population is approximately normal. Copy Data Step 2 of 4: Calculate the sample standard deviation for the given sample data. Round your answer to two decimal places.