The perimeter of a rectangle is 18 cm, the length is 5 cm, and the width is in cm.
一个长方形的周长是18厘米，长是5厘米，宽是多少厘米．
<gadget id="calculator">18 / 2</gadget>
<output>9</output>

<gadget id="calculator">9 - 5</gadget>
<output>4</output>

<result>4</result>