Several chickens and rabbits are used in a cage, with 40 heads from the top and 100 feet from the bottom. Which of the following statements is correct is how many rabbits are in the cage
笼子里用若干只鸡和兔，上面看有40个头，下面看有100只脚．下面说法正确的是笼子里有多少只兔
<gadget id="calculator">40 * 4</gadget>
<output>160</output>

<gadget id="calculator">160 - 100</gadget>
<output>60</output>

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

<gadget id="calculator">60 / 2</gadget>
<output>30</output>

<gadget id="calculator">40 - 30</gadget>
<output>10</output>

<result>10</result>