From the top of a building of height 20m, the angles of depression of the top and bottom of a tower are $$30^\circ, 60^\circ$$ respectively. Then the height of the tower. in meters, is

A

$$15\frac{1}{3}$$

B

$$13\frac{1}{3}$$

C

$$11\frac{1}{3}$$

D

$$9\frac{1}{3}$$