A truck goes from Haryana to Bangalore with an average speed of 60 km/h. The journey takes 30 hours. It returns from Bangalore to Haryana on the same road with an average speed of 40 km/h. What was the average speed of the truck during the roundtrip?

A

60 km/h

B

40 km/h

C

50 km/h

D

48 km/h