The perimeter of a rectangle is 20 meters, the length is 6 meters, and the width is in meters.
长方形周长20米，长6米，宽多少米．
<gadget id="calculator">20 / 2</gadget>
<output>10</output>

<gadget id="calculator">10 - 6</gadget>
<output>4</output>

<result>4</result>