Two squares with side lengths of 3 cm are put together to form a rectangle. What is the perimeter of the rectangle in cm?
两个边长是3cm的正方形拼成一个长方形，这个长方形的周长是多少cm．
<gadget id="calculator">3 + 3 + 3</gadget>
<output>9</output>

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

<result>18</result>