A rectangular vegetable field is surrounded by a bamboo fence (fences are used on four sides). It is known that the length of the bamboo fence is 12 meters. What is the maximum area of the vegetable field enclosed?
用竹篱笆围一块长方形菜地(四边用篱笆)，已知竹篱笆长12米，围成的菜地面积最大是多少．
<gadget id="calculator">12 / 4</gadget>
<output>3</output>

<gadget id="calculator">3 * 3</gadget>
<output>9</output>

<result>9</result>