What is the area of a square with a perimeter of 20 cm?
周长是20厘米的正方形，面积是多少平方厘米．
<gadget id="calculator">20 / 4</gadget>
<output>5</output>

<gadget id="calculator">5 * 5</gadget>
<output>25</output>

<result>25</result>