The distance between A and B is 6 kilometers. A person walks from A to B. The first half of the time averages 80 meters per minute, and the second half of the time averages 70 meters per minute. Ask him how many minutes it took for 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．问他走后一半路程用了多少分钟？
<gadget id="calculator">80 + 70</gadget>
<output>150</output>

<gadget id="calculator">6_000 / 150</gadget>
<output>40</output>

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

<gadget id="calculator">6_000 / 2 / 80</gadget>
<output>75/2 = around 37.5</output>

<gadget id="calculator">80 - (75/2)</gadget>
<output>85/2 = around 42.5</output>

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