Chlorine in drinking water is a possible health risk. A recent article reported chlorine concentrations in drinking water in parts per billion for 10 urban communities and 10 rural communities. Urban: 3, 7, 25, 10, 15, 6, 12, 25, 7. Rural: 48, 44, 40, 38, 33, 21, 20, 12, 1, 18. Construct a 90% confidence interval for u1 u2. Assume that the samples come from normal populations with unknown and different variance