What is the area of a square with a perimeter of 40 decimeters?
周长为40分米的正方形，面积是多少平方分米．
<gadget id="calculator">40 / 4</gadget>
<output>10</output>

<gadget id="calculator">10 * 10</gadget>
<output>100</output>

<result>100</result>