Truck a
V = 68km/h
t = 2hours
Distance = speed * time
D = 68 * 2
D = 136km
Truck B
Speed = 57km/h
t = 2 hours
Distance = speed * time
D = 57 * 2
D = 114km
Distance travelled by truck A = 136 km
Distance travelled by truck B = 114km
Distance apart = 136km - 114km = 22km
Hence both the trucks will be 22kms apart.
Hope this helps. Plz let me know if you have any doubts.