The concentration of benzere was measured in units of milligram per her for a simple rando sample of five specimera of untreated wastewater produced at a gas field. The sample mean was 78 sample standard deviation of 1.4. Seven specimens of treated wastewater had a benzene concentration sample mean of 3.2 with standard deviation of 1.7, Assume that both samples com from populations with approximately normal distributions Constructa 99% confidence interval for a where a represents the population mean for untreated wastewater and pas represents the population mean for treated wastewater