Independent random samples from 2 normally distributed populations give the following results

n_x= 10 x=480 s_x=30

n_y= 12 y= 520 s_y= 25

A) If we assume that the unknow population variances are equal , what is the 90% confidence interval for the difference OF population means?

B) If we assume that the unknow population variances are equal , what is the 90% confidence interval for the difference BETWEEN population means?

OF vs. BETWEEN? Where is the difference? What is he asking? I just know a formula that is (x-y) + or - t* sqroot [(s2_p/n_x) + (s2_p/n_y) ]

Help. Please.