Two **** merchants arrive at the gates of Paris. One has 64 and the other 20 barrels of ****. Since they have not enough money to pay the custom duties, the first pays 40 francs and 5 barrels of ****. The second pays 2 barrels of **** but receives 40 francs in change.What is the value of each barrel of **** and what is the duty payable? -Riddles