The highway fuel economy of a 2022 Hyundai Sonata automatic 5-speed using a fuel is normally distributed with a unknown standard deviation. If a sample data of 10 trips yields a mean of 28.0 mpg and a sample standard deviation of 1.23 mpg, find the 99 percent confidence interval for the true mean mpg. (Note: mpg represents 'miles per gallon', which is used as a measure of fuel economy)

ex) 23.123 +_ 3.213