The width of a rectangle is 4 meters and the length is twice the width. What is the perimeter of the rectangle?
一个长方形的宽是4米，长是宽的2倍，这个长方形的周长是多少．
<gadget id="calculator">4 * 2</gadget>
<output>8</output>

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

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

<result>24</result>