Xiao Ming and Xiao Liang walk along a circular lake with a radius of 500 meters at the same time from the same place with their backs. Xiao Ming travels 81 meters per minute, and Xiao Liang travels 76 meters per minute. How many minutes did it take for the two to meet?
小明和小亮，沿着半径500米的圆形湖边，同时从同一地点，背向而行，小明每分钟行81米，小亮每分钟行76米，经过多少分钟两人相遇？
<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>