History homework help

study of the career paths of hotel general managers sent questionnaires to an SRS of 180 hotels belonging to major U.S. hotel chains. There were 118 responses. The average time these 118 general managers had spent with their current company was 11.1 years. Give a 99% confidence interval for the mean number of years general managers of major-chain hotels have spent with their current company. (Take it as known that the standard deviation of time with the company for all general managers is 4.5 years.)