If two squares with an area of 9 square centimeters are put together to form a rectangle, what is the perimeter of the rectangle?
把两个面积是9平方厘米的正方形拼成一个长方形，长方形的周长是多少．
<gadget id="calculator">3 + 3</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>