A square chicken coop is 6 meters long, one side is against the wall, and three sides are surrounded by fences. How long does the fence need to be?
一个正方形的鸡舍边长是6米，一面靠墙，三面用篱笆围起来．需要准备多长的篱笆？
<gadget id="calculator">6 * 3</gadget>
<output>18</output>

<result>18</result>