A rectangle with a length of 30 cm and a width of 20 cm is equal to the perimeter of a square. What is the area of the square in square centimeters?
一个长方形，长30厘米，宽20厘米，与一个正方形的周长相等，这个正方形的面积是多少平方厘米？
<gadget id="calculator">30 + 20</gadget>
<output>50</output>

<gadget id="calculator">50 * 2</gadget>
<output>100</output>

<gadget id="calculator">100 / 4</gadget>
<output>25</output>

<gadget id="calculator">25 * 25</gadget>
<output>625</output>

<result>625</result>