A professional poultry farmer wants to use a 24-meter-long fence to form a rectangular chicken farm. How to enclose the chicken farm can have the largest area, and how many square meters is the largest area?
一个养禽专业户想用一段长24米的篱笆一面靠墙围成一个长方形养鸡场，如何围这鸡场面积才能最大，最大的面积是多少平方米．
<gadget id="calculator">6 * 2</gadget>
<output>12</output>

<gadget id="calculator">24 - 12</gadget>
<output>12</output>

<gadget id="calculator">12 * 6</gadget>
<output>72</output>

<result>72</result>