Given that the width of the rectangle is 4 cm and the length is twice the width, what is the perimeter of the rectangle?
已知长方形的宽为4厘米，长是宽的2倍，求长方形的周长？
<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>