The distance between A and B is 6 kilometers. A person walks from A to B. He walks an average of 80 meters per minute in the first half of the time, and an average of 70 meters per minute in the second half of the time. How long does it take him to walk the second half of the journey?
甲乙两地相距6千米，某人从甲地步行去乙地，前一半时间平均每分钟行80米，后一半时间平均每分钟行70米，问他走后一半行程用了多长时间？
<gadget id="calculator">200 / 80</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">(5/2) + 40</gadget>
<output>85/2 = around 42.5</output>

<result>85/2 = around 42.5</result>