During a journey of 120 km, Rahi drives first 60 km at the speed of 60 km/h, next 30 km at 60 km/h and the remaining 30 km at the speed of 30 km/h. Determine the average speed.

A

48 km/h

B

33.33 km/h

C

50 km/h

D

40 km/h