The monthly salaries, w dollars, of 10 women are such that (w 3000) = 200. The

The monthly salaries, w dollars, of 10 women are such that ­Σ(w − 3000) = −200.

The monthly salaries, m dollars, of 20 men are such that ­ Σ(m − 4000) = 120.

a. Find the difference between the mean monthly salary of the women and the mean monthly salary of the men.

b. Find the mean monthly salary of all the women and men together.