There is a rectangular vegetable field surrounded by a fence, which is 9 meters wide and 3 meters shorter than the length. What is the total length of the rectangular fence?
有一块用篱笆围成的长方形菜地，宽9米，比长短3米，围成长方形的篱笆全长多少米？
<gadget id="calculator">9 + 9 + 3</gadget>
<output>21</output>

<gadget id="calculator">21 * 2</gadget>
<output>42</output>

<result>42</result>