Uncle Zhang’s family has a rectangular vegetable field, 8 meters long and 4 meters wide, surrounded by a fence. How long is the fence?
张伯伯家有一块长方形菜地，长8米，宽4米，四周围上篱笆，篱笆长多少米？
<gadget id="calculator">8 + 4</gadget>
<output>12</output>

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

<result>24</result>