Plant trees around a circular pool at intervals of 3 meters. A total of 20 trees are planted. What is the circumference of the pool in meters?
在一个圆形水池的四周种树，每隔3米种一棵，一共种了20棵，这个水池的周长是多少米．
<gadget id="calculator">20 * 3</gadget>
<output>60</output>

<result>60</result>