If the perimeter of a square is 20 cm, what is the area in square centimetres?
一个正方形周长是20cm，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>