If two squares have sides 3 cm long, what is the perimeter of the resulting rectangle?
两个边长是3厘米的正方形，拼成的长方形的周长是多少厘米．
<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>