The distance between A and B is 900 meters. A and B travel from A to B at the same time. A travels 70 meters per minute, and B travels 50 meters per minute. When A arrives at B, he returns immediately and meets B on the way. How many minutes have passed since we met?
AB两地相距900米，甲、乙两人同时从A到B，甲每分钟行70米，乙每分钟行50米，当甲到达B后立即返回与乙在途中相遇，两人从出发到相遇共经过多少分钟？
<gadget id="calculator">70 + 50</gadget>
<output>120</output>

<gadget id="calculator">2 / 120</gadget>
<output>1/60 = around 0.016667</output>

<gadget id="calculator">900 * (1/60)</gadget>
<output>15</output>

<result>15</result>