Contaminated water: The concentration of benzene was measured in units of milligrams per liter for a simple random sample of five specimens of untreated wastewater produced at a gas field. The sample mean was 7.8 with a sample standard deviation of 1.4. Seven specimens of treated wastewater had an average benzene concentration of 3.2 with a standard deviation of 1.7. Assume that both samples come from normal populations. Can you conclude that the standard deviation of benzene concentration differs between treated water and untreated water? Use the a = 0.05 level of significance.