Xiaohua and Xiaojun walk away from the same point along a circular lake with a radius of 500 meters. Xiaohua walks 81 meters per minute, and Xiaojun walks 76 meters per minute. How many minutes did it take for the two to meet?
小华和小军沿着一个半径是500米的圆形湖边同时从同一点相背而行．小华每分钟行81米，小军每分钟行76米．两人经过多少分钟相遇？
<gadget id="calculator">2 * 3.14 * 500</gadget>
<output>3_140</output>

<gadget id="calculator">81 + 76</gadget>
<output>157</output>

<gadget id="calculator">3_140 / 157</gadget>
<output>20</output>

<result>20</result>