There is a rectangular vegetable field with a length of 20 meters. If its length is reduced by 6 meters, the area will be reduced by 240 square meters. Find the area of this rectangular vegetable plot?
有一个长方形菜地，长是20米，如果把它的长减少6米，面积减少240平方米．求这个长方形菜地的面积？
<gadget id="calculator">240 / 6</gadget>
<output>40</output>

<gadget id="calculator">20 * 40</gadget>
<output>800</output>

<result>800</result>