Find the perimeter of a rectangle made of two squares with side lengths of 6 cm.
用两个边长为6厘米的正方形拼成一个长方形，求这个长方形的周长．
<gadget id="calculator">6 * 2</gadget>
<output>12</output>

<gadget id="calculator">12 + 6</gadget>
<output>18</output>

<gadget id="calculator">18 * 2</gadget>
<output>36</output>

<result>36</result>