Help solving problem

(6) Construct a confidence interval for ua, the mean of the differences d for the population of paired data. Assume that the population of paired differences is normally distributed. Ten different families are tested for the number of gallons of water a day they use before and after viewing a conservation video. Construct a 90% confidence interval for the mean of the differences. Before 33 33 38 33 35 35 40 40 40 31 After 34 28 25 28 35 33 31 28 35 33