A levee was built around a lake. Poplars were planted every 20 meters on the levee, and 3 willows were planted between two adjacent poplars. There were 1,200 willows in total. How long is the levee?
在一条湖泊周围筑了一条大堤，堤上每隔20米种一棵杨树，相邻两棵杨树之间种了3棵柳树，这样共种柳树1200棵，这条大堤长多少米？
<gadget id="calculator">1_200 / 3</gadget>
<output>400</output>

<gadget id="calculator">20 * 400</gadget>
<output>8_000</output>

<result>8_000</result>