A 2-meter-long iron wire surrounds a square with a side length of 3 decimeters, how many decimeters are left?
用一根2米长的铁丝围成一个边长为3分米的正方形，还剩多少分米？
<gadget id="calculator">2 * 10</gadget>
<output>20</output>

<gadget id="calculator">3 * 4</gadget>
<output>12</output>

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

<result>8</result>