One day a young man came to Boss Wang's store and bought a gift. The cost of this gift was 18 yuan, and the price was 21 yuan. It turned out that the young man took out 100 yuan to buy this gift. Boss Wang had no change at the time, so he exchanged the 100 yuan for 100 yuan change from the neighbor, and gave the young man 79 yuan. But the neighbor later found out that the 100 yuan was a counterfeit bill, and Boss Wang had no choice but to return the 100 yuan to the neighbor. Now the question is: how much money did Boss Wang lose in this transaction?
一天有个年轻人来到王老板的店里买了一件礼物，这件礼物成本是18元，标价是21元．结果是这个年轻人掏出100元要买这件礼物，王老板当时没有零钱，用那100元向街坊换了100元的零钱，找给年轻人79元．但是街坊后来发现那100元是假钞，王老板无奈还了街坊100元．现在问题是：王老板在这次交易中到底损失了多少元钱．
<gadget id="calculator">18 + 79</gadget>
<output>97</output>

<result>97</result>