A car travels $$\frac{1}{3}$$ of the distance on a straight road at a speed of 10 km/h, the next $$\frac{1}{3}$$ at a speed of 20 km/h and the last $$\frac{1}{3}$$ at a speed of 60 km/h. Find the average speed of the car.

A

18 km/h

B

15 km/h

C

12 km/h

D

10 km/h