A, B, and C are walking on the road from school to the park. A walks 12 meters more per minute than B, and B walks 9 meters more than C per minute. The three started from the school at the same time at 8:00 a.m. A arrived at the park at 9:00 a.m. and returned to the school immediately, and met B at a distance of 420 meters from the park. How long will A and C meet again?
甲、乙、丙三人在学校到公园的路上散步，甲每分钟比乙多走12米，乙每分钟比丙多走9米．上午8点三人同时从学校出发，上午9点甲到达公园后立即返回学校，在距公园420米处遇到乙．再过多长时间甲与丙相遇？
<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">2_520 * 2</gadget>
<output>5_040</output>

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

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

<gadget id="calculator">5_040 / 63</gadget>
<output>80</output>

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

<result>10</result>