Assume: actual worth of item is 6. Now, realize that the tobacconist is extraneous information. How can I say that? Well, he has no net gain or loss. He might as well be the cash register. Forget him. He gives money, then he gets the same amount. For that matter, it doesn't matter that the person gives the conman a box of chocolates and 4 shillings. Just say he gives him 10 shillings. That puts the situation this way: the seller gave the conman 10 shillings, while the conman gave the owner nothing. Net Loss = 10 shillings Ta Da!