3 squares with side lengths of 3 cm are used to form a rectangle. What is the perimeter of the rectangle in cm?
用3个边长为3厘米的正方形拼成一个长方形，这个长方形的周长为多少厘米．
<gadget id="calculator">3 + 3 + 3</gadget>
<output>9</output>

<gadget id="calculator">9 + 3</gadget>
<output>12</output>

<gadget id="calculator">12 * 2</gadget>
<output>24</output>

<result>24</result>