Ten specimens of untreated wastewater produced at a gas field had an average benzene concentration of 6.83 mg/L with a standard deviation of 1.72 mg/L. Seven specimens of treated waste water had an average benzene concentration of 3.32 mg/L with a standard deviation of 1.17 mg/L. Let μX represent the population mean for untreated wastewater and let μY represent the population mean for treated wastewater. Find a 95% confidence interval for the difference μX−μY . Round down the degrees of freedom to the nearest integer and round the answers to three decimal places. The 95% confidence interval is ( , ).