solve asap

As part of an annual review of its accounts, a discount brokerage selects a random sample of 18 customers. Their accounts are reviewed for total account valuation, which showed a mean of $40,000, with a sample standard deviation of $9000. What is a 80 confidence interval for the mean account valuation of the population of customers? (Round the final answers to the nearest who dollar.) 80% confidence interval for the mean account valuation is between $ and $