The width of a rectangular piece of paper is 4 cm, and the length is twice the width. What is the perimeter of the rectangle in cm?
一张长方形纸的宽是4厘米，长是宽的2倍，这个长方形的周长是多少厘米．
<gadget id="calculator">4 * 2</gadget>
<output>8</output>

<gadget id="calculator">4 + 8</gadget>
<output>12</output>

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

<result>24</result>