Motorcycles ahead of time cars are:

9 hours - 8 hours 24 minutes = 36 minutes

Change: 36 minutes = 0.6 hours

When cars start to go, two cars are separated:

36 x 0.6 = 21.6 (km)

The velocity of the two vehicles is:

54 - 36 = 18 (km / h)

Automobile catch up motorcycles after the time is:

21.6: 18 = 1.2 (hour)

The long AB distance is:

54 x 1.2 = 64.8 (km)

Answer ; 64,8 km