A square has a perimeter of 80 cm. What is the area of this square in square centimetres.
一个正方形周长80厘米．这个正方形的面积是多少平方厘米．
<gadget id="calculator">80 / 4</gadget>
<output>20</output>

<gadget id="calculator">20 * 20</gadget>
<output>400</output>

<result>400</result>