There are x roosters, 9 hens are twice as many as roosters, 33 hens, how many roosters are there?
公鸡x只，母鸡比公鸡的2倍还少9只，母鸡33只，公鸡有几只？
<gadget id="calculator">33 + 9</gadget>
<output>42</output>

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

<result>21</result>