A man divided his journey into three parts of distances of 18 km, 20 km and 27 km. He travelled the distances at the speeds of 6 km/h, 5 km/h and 9 kn/h,respectively. What was his average speed during the entire journey?

A

6.5 km/h

B

4.5 km/h

C

7.5 km/h

D

5.5 km/h