Calculate the perimeter of a rectangle with a length of 4 cm and a width of 2 cm.
计算长4厘米，宽2厘米的长方形的周长．
<gadget id="calculator">4 + 2</gadget>
<output>6</output>

<gadget id="calculator">6 * 2</gadget>
<output>12</output>

<result>12</result>