rectangular vegetable field is 18 meters long and 9 meters wide, surrounded by bamboo fences. How long is the bamboo fence?
一块长方形菜地，长18米，宽9米，要在周围围上竹篱笆．竹篱笆长多少米？
<gadget id="calculator">18 + 9</gadget>
<output>27</output>

<gadget id="calculator">27 * 2</gadget>
<output>54</output>

<result>54</result>