A second-grade math question is not suitable for business

I have always been good at doing smart questions. I was wrong at the first time.SohoLife is a blow (joke )! Paste it to see how many people can answer the question. Of course, the question is relatively simple after all, no paper or pen, the time limit is 5 minutes. It is said that5The answer within minutes is wrong, proving that you are not suitable for business !!

The questions are as follows:

 

One day, a young man came to Wang's store to buy a gift. The cost of this gift is 18 RMB. The price is 21 RMB. The result is that the young man took out 100 Yuan wants to buy this gift. Boss Wang didn't have any change at the time. 100 Yuan xiangjiefang changed 100 Yuan change, for young people 79 RMB. But I found out that 100 Yuan is a fake banknote, and Boss Wang has no choice but to pay back the street 100 RMB. Now the question is: How much money does Boss Wang lose in this transaction? ?