The distance between A and B is 600 kilometers. Two people, A and B, start from A to B by bicycle at the same time. A rides 40 kilometers a day, B rides 60 kilometers a day, but B rides one day and rests one day. At the end of the journey on the number of days, the distance from B to B is twice the distance from A to B.
A，B两地相距600千米，甲、乙两人同时骑自行车从A地出发去B地．甲每天骑40千米，乙每天骑60千米，但乙骑一天休息一天．第多少天的行程结束时，乙距B地的路程是甲距B地的路程的二倍．
<gadget id="calculator">2 * 600</gadget>
<output>1_200</output>

<gadget id="calculator">1_200 - 600</gadget>
<output>600</output>

<gadget id="calculator">2 * 40</gadget>
<output>80</output>

<gadget id="calculator">60 / 2</gadget>
<output>30</output>

<gadget id="calculator">80 - 30</gadget>
<output>50</output>

<gadget id="calculator">600 / 50</gadget>
<output>12</output>

<result>12</result>