Use a 60-meter-long fence to surround a rectangle against the wall to raise chickens. What is the maximum area of the chicken farm?
用60米长的篱笆靠墙围一个长方形用来养鸡，养鸡场的面积最大是多少？
<gadget id="calculator">30 * 15</gadget>
<output>450</output>

<result>450</result>