According to a study, several years ago by the Emerson Communications Industry Association, the average wireless phone user earns $ 62,600 per year. Suppose a researcher believes that the average annual earnings of a wireless phone user are lower now, and sets up a study in an attempt to prove his theory. He randomly selects 38 wireless phone users and finds out that the average annual salary for this sample is $58794, with a population standard deviation of $7810. Use α = 0.01 to test the researcher's theory. Assume wages in this industry are normally distributed, determine the 99% confidence interval of the population mean.