The perimeter of a rectangular pond is 300 meters. Its length is 100 meters, what is its width?
一个长方形池塘的周长是300米．它的长是100米，宽是多少米？
<gadget id="calculator">300 / 2</gadget>
<output>150</output>

<gadget id="calculator">150 - 100</gadget>
<output>50</output>

<result>50</result>