With individual lines at its various windows, a post office finds that the standard deviation for waiting times for customers on friday afternoon is 8.0 minutes. the post office experiments with a single, main waiting line and finds that for a random sample of 20 customers, the waiting times for customers have a standard deviation of 3.1 minutes on a friday afternoon. with a significance level of 5%, test the claim that a single line causes lower variation among waiting times for customers. just perform step of the hypothesis testing process - calculate the test statistic. perform calculation to 3 decimal places.