A man jogging inside a railway tunnel at a constant speed hears a train approaching the tunnel from behind at a speed of 30km/h, when he is one third of the way inside the tunnel. Whether he keeps running forward or turns back, he will reach the end of the tunnel at the same time the train reaches that end. The speed at which the man is running is:

A.

6 km/hr

B.

8 km/hr

C.

12 km/hr

D.

10 km/hr