A rectangle and a square have the same perimeter. It is known that the perimeter of the square is 60 decimeters. If the length of the rectangle is 20 decimeters, what is the area of the rectangle?
一个长方形和一个正方形的周长相等，已知正方形的周长是60分米，如果长方形的长是20分米，这个长方形的面积是多少平方分米？
<gadget id="calculator">60 / 2</gadget>
<output>30</output>

<gadget id="calculator">30 - 20</gadget>
<output>10</output>

<gadget id="calculator">20 * 10</gadget>
<output>200</output>

<result>200</result>