The round flower bed of the school is planted every 2 meters a week, and a total of 15 trees have been planted. What is the circumference of the flower bed in meters?
学校圆形花坛一周每隔2米种一棵数，共种了15棵，花坛周长是多少米
<gadget id="calculator">2 * 15</gadget>
<output>30</output>

<result>30</result>