AARP reported on a study conducted of the mean time it takes individuals to prep

AARP reported on a study conducted of the mean time it takes individuals to prepare their federal income tax return. The data contained in the file named TaxReturn are consistent with the study results. These data provide the time in hours required for 40 individuals to complete their federal income tax returns. Using past years data the population standard deviation can be assumed known with =9 hours. What is the 95% confidence interval estimate of the mean time it takes an individual to complete a federal income tax return?