There are 24 chickens and rabbits. There are 54 legs. How many of them are chickens?
鸡和兔共24只，数一数腿有54条，其中鸡有多少只．
<gadget id="calculator">24 * 4</gadget>
<output>96</output>

<gadget id="calculator">96 - 54</gadget>
<output>42</output>

<gadget id="calculator">4 - 2</gadget>
<output>2</output>

<gadget id="calculator">42 / 2</gadget>
<output>21</output>

<result>21</result>