A person has to make a journey of 72 km. He rides a cycle at 12 km/hr. After going a certain distance the cycle is punctured and he walks the remaining distance at 4 1/2 km/hr. Find where the cycle is punctured if the total time for the journey is 81/2 hours.

A

50 km

B

52 km.

C

54 km

D

56 km