9 5 points Contaminated water The concentration of benzene was measured in units of milligrams per liter for a simple random sample of seven specimens of untreated wastewater produced at a gas field The sample mean was 7 7 with a sample standard deviation of 1 3 Nine specimens of treated wastewater had an average benzene concentration of 3 5 with a standard deviation of 1 5 It is reasonable to assume that both samples come from populations that are approximately normal Construct a 95 confidence interval for the reduction in benzene concentration after treatment Use the TI 84 calculator and round the answers to one decimal place