g According to the United States Postal Service, First Class Mail International (letters) takes 6 to 20 days to deliver to their destination. In order to test this, Greg, in Chicago, sent one letter to Madrid, Spain every Monday for 52 weeks and tracked how long each letter took to deliver. The average delivery time for these 52 letters was 11.81 days and with a sample standard deviation of 3.17. Calculate a 90% confidence interval for the true mean delivery time of First Class Mail International letters from Chicago to Madrid.