Ao Zebra, Ou Ou, and Xiao Mei are walking on the way from school to the park. Ao Zebra walks 12 meters more per minute than O Ou, and O Ou walks 9 meters more per minute than Xiao Mei. The three of them set off from the school at the same time at 8:00 a.m. Ao Zebra arrived at the park at 9:00 a.m. and returned to the school immediately, and met Ou Ou at a distance of 420 meters from the park. So, how long will it take for Ao Zebra and Xiaomei to meet?
奥斑马、欧欧、小美三人在学校到公园的路上散步，奥斑马每分钟比欧欧多走12米，欧欧每分钟比小美多走9米．上午8点三人同时从学校出发，上午9点奥斑马到达公园后立即返回学校，在距公园420米处遇到欧欧．那么，再过多长时间奥斑马与小美相遇？
<gadget id="calculator">420 * 2</gadget>
<output>840</output>

<gadget id="calculator">840 / 12</gadget>
<output>70</output>

<gadget id="calculator">70 - 60</gadget>
<output>10</output>

<gadget id="calculator">420 / 10</gadget>
<output>42</output>

<gadget id="calculator">42 * 60</gadget>
<output>2_520</output>

<gadget id="calculator">42 - 12 - 9</gadget>
<output>21</output>

<gadget id="calculator">42 + 21</gadget>
<output>63</output>

<gadget id="calculator">2 / 63</gadget>
<output>2/63 = around 0.031746</output>

<gadget id="calculator">2_520 * (2/63)</gadget>
<output>80</output>

<gadget id="calculator">80 - 70</gadget>
<output>10</output>

<result>10</result>