Situation

A tank is supplied by two pipes A and B and emptied by a third pipe C. If the tank is empty and all pipes are opened, the tank can be filled in 20 hours. If the tank is full and A and C are opened, the tank can be emptied in 4 hours. If the tank is full and B and C are opened, the tank can be emptied in 2 hours. Pipe A supplies 50 liters per minute more than B.