It costs 12 yuan to buy a chair, to buy a table for the price of two chairs, and to buy a bookcase for the price of three tables. How much is a bookcase.
买一把椅子需要12元，买两把椅子的价钱可以买一张桌子，买3张桌子的价钱可买一只书橱．一个书橱多少元．
<gadget id="calculator">12 * 2</gadget>
<output>24</output>

<gadget id="calculator">24 * 3</gadget>
<output>72</output>

<result>72</result>