The perimeter of a rectangle is 20 cm, the length is 6 cm, and the width is in cm.
一个长方形周长是20厘米，长6厘米，宽是多少厘米．
<gadget id="calculator">20 / 2</gadget>
<output>10</output>

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

<result>4</result>