The problem states that the car consumes 6.8 liters of gasoline per 100 km. It also mentions two different routes requiring the same amount of gasoline. The question asks how many liters of gasoline the car consumes per 100 km on the 'problematic roads'. Since the consumption rate is given as 6.8 liters per 100 km, and the routes are stated to use the same volume of gasoline, the consumption on the 'problematic roads' is also 6.8 liters per 100 km.