Distance between A and B=120 km
Speed of car starting from A=120/6
Speed of car starting from B=distance/speed of car starting from A=120/20
The above solution is for the same direction.
Time taken when cars running in opposite direction=4320 seconds
Speed of both the cars=120000 m/4320 seconds.
The speed of the cars are the same becuase of the direction of the cars.