Given that two tankers contains 850 liters and 680 liters of petrol. The maximum capacity of tankers which can measure the petrol of either tankers in exact number of times should have the volume equal to the sum in liters of the petrol in both tankers. Thus the sum will give us:
850+680
=1,530 liters
Therefore, the volume of the tanker that can measure the amount of petrol in exact number of times should have a volume of 1,530 liters