The weight of 1 book = the weight of 2 bottles of milk, the weight of 1 bottle of milk = the weight of 5 moon cakes, the weight of 3 books = the weight of how many moon cakes.
1本书的重量=2瓶牛奶的重量，1瓶牛奶的重量=5个月饼的重量，3本书的重量=多少个月饼的重量．
<gadget id="calculator">6 * 5</gadget>
<output>30</output>

<result>30</result>