The perimeter of the rectangle is 280 meters, its length is 100 meters, what is its area in square meters?
长方形的周长是280米，已知它的长是100米，它的面积是多少平方米？
<gadget id="calculator">280 / 2</gadget>
<output>140</output>

<gadget id="calculator">140 - 100</gadget>
<output>40</output>

<gadget id="calculator">100 * 40</gadget>
<output>4_000</output>

<result>4_000</result>