A square of cardboard is 6 cm long. Fold it in half and cut it. What is the perimeter of each rectangle?
一个正方形硬纸长6厘米，对折后剪开，每个长方形的周长是多少．
<gadget id="calculator">6 / 2</gadget>
<output>3</output>

<gadget id="calculator">6 + 3</gadget>
<output>9</output>

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

<result>18</result>