If the length of a rectangle is 6 meters and the width is 3 meters, what is the perimeter of the rectangle?
一个长方形的长为6米，宽为3米，长方形的周长为多少．
<gadget id="calculator">6 + 3</gadget>
<output>9</output>

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

<result>18</result>