A rectangular wooden sign is 3 decimeters wide and twice as long as it is wide. What is the minimum length of ribbon needed to decorate the wooden sign beautifully with ribbons?
一块长方形的木牌，它的宽是3分米，长是宽的2倍．要把木牌用彩带在周围装饰得漂亮一些，至少需要多长的彩带？
<gadget id="calculator">3 * 2</gadget>
<output>6</output>

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

<gadget id="calculator">9 * 2</gadget>
<output>18</output>

<result>18</result>