The random variables A and B follow normal distribution, A has a standard deviation phi 1 = 6, and B has a standard deviation of phi 2 =4. Take a sample size of 20 from each random variable, we obtained X1(there's a line over the x) = 80 and X2 (there a line over the x) = 85

(a) Find a 95% confidence interval for the mean difference u1-u2.

(b) can you conclude that the mean of the variable B is higher than mean of A?