A rectangular vegetable field is 7 meters long and 5 meters wide, surrounded by a fence. How long is the fence?
一块长方形菜地，长7米，宽5米，四周围上篱笆，篱笆长多少米？
<gadget id="calculator">7 + 5</gadget>
<output>12</output>

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

<result>24</result>