Use a fence to form a rectangular chicken farm. Use an 18-meter-long wall on one side. The total length of the fence is 40 meters. Find the area of the chicken farm.
用篱笆围成一个长方形的养鸡场，一边利用18米长的墙壁，篱笆共长40米，求养鸡场的面积．
<gadget id="calculator">40 - 18</gadget>
<output>22</output>

<gadget id="calculator">22 / 2</gadget>
<output>11</output>

<gadget id="calculator">11 * 18</gadget>
<output>198</output>

<result>198</result>