Bob Nale is the owner of Nale's Texico. Bob would like to estimate the mean number of gallons of gasoline sold to his customers. Assume the mean number of gallons of gasoline follows a normal distribution with a standard deviation of 2.30 gallons. From the records he selects a random sample of 60 customers and finds the mean number of gallons is 9.60. Develop a 99 percent confidence interval for the population.