One third of a certain journey is covered at the rate of 25 km/hour, one-fourth at the rate of 30 $$\frac{km}{hour}$$ and the rest at 50 $$\frac{km}{hour}$$ . The average speed for the whole journey is

A

35 $$\frac{km}{hour}$$

B

33 $$ \frac{1}{3} \frac{km}{hour}$$

C

30 $$\frac{km}{hour}$$

D

37 $$ \frac{1}{12} \frac{km}{hour}$$