A pet store only sells parrots and rabbits. All pets have 20 heads and 56 legs. How many rabbits are there in this store?
一宠物店只卖鹦鹉及兔子，所有宠物合共有头20个，脚56只，该店内共有兔子多少只？
<gadget id="calculator">20 * 4</gadget>
<output>80</output>

<gadget id="calculator">80 - 56</gadget>
<output>24</output>

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

<gadget id="calculator">24 / 2</gadget>
<output>12</output>

<gadget id="calculator">20 - 12</gadget>
<output>8</output>

<result>8</result>