What a loss?
A woman purchased a pair of shoes at $20 whose cost price for shopkeeper(SK-1) was $15. She gave him a $100 note. SK-1 was not having change to return. He took change of $100 from the fellow shopkeeper(SK-2). He came back and returned $80 to woman. In the evening, the SK-2 comes back and says " Note which you gave me is fake. Return me my money". SK-1 returns him back $100. How much is the total loss for SP-1 in the whole transaction?