Suppose that a random sample of 19 recently sold houses in a certain city has a mean sales price of $280,000, with a standard deviation of $6000. Under the assumption that house prices are normally distributed, find a 99% confidence interval for the mean sales price of all houses in this city. Give the lower limit and upper limit of the 99% confidence interval. Carry your intermediate computations to at least three decimal places. Round your answers to the nearest whole number. (If necessary, consult a list of formulas.) Lower limit: $ X Upper limit: $