A rectangle with a length of 6 cm is surrounded by an iron wire with a length of 18 cm. What is the width of the rectangle in cm?
用一根长18厘米的铁丝围成一个长为6厘米的长方形，这个长方形的宽是多少厘米？
<gadget id="calculator">18 / 2</gadget>
<output>9</output>

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

<result>3</result>