A rectangle with a perimeter of 18 cm has a length of 6 cm and a width of 6 cm.
周长为18厘米的长方形，长是6厘米，宽是多少厘米．
<gadget id="calculator">18 / 2</gadget>
<output>9</output>

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

<result>3</result>