As part of an annual review of its accounts, a discount brokerage selects a random sample of 30 customers. Their accounts are reviewed for total account valuation, which showed a mean of $21,000, with a sample standard deviation of $7500. What is a 90% confidence interval for the mean account valuation of the population of customers? (Round the final answers to the nearest whole dollar.)

90% confidence interval for the mean account valuation is between $ and $ .