If the length of a rectangle is 6 cm and the circumference is 20 cm, what is its width in cm?
一个长方形的长是6厘米，周长是20厘米，它的宽是多少厘米．
<gadget id="calculator">20 / 2</gadget>
<output>10</output>

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

<result>4</result>