I need help with this with full and very clear explanation

1. The values listed below are waiting times (in minutes) of customers at the CB&T Bank, where customers enter a single waiting line that feeds three teller windows. Construct a 95% confidence interval for the population standard deviation o. Round the answers in the confidence intervals to three decimal places. 6.5 6.6 6.7 6.9 7.3 7.5 7.5 7.7 7.7 7.7