A rectangular flower bed is 20 meters wide, and there is a railing around the flower bed. The length of the fence is 100 meters. What is its area?
一个长方形花坛宽是20米，在花坛的四周围一圈栏杆，围栏的长度是100米，它的面积是多少？
<gadget id="calculator">100 / 2</gadget>
<output>50</output>

<gadget id="calculator">50 - 20</gadget>
<output>30</output>

<gadget id="calculator">30 * 20</gadget>
<output>600</output>

<result>600</result>