The perimeter of a rectangle is 18 meters, its length is 6 meters, and its width is in meters.
一个长方形的周长是18米，它的长是6米，宽是多少米．
<gadget id="calculator">18 / 2</gadget>
<output>9</output>

<gadget id="calculator">9 - 6</gadget>
<output>3</output>

<result>3</result>