The distance between AB and AB is 8 kilometers. Xiao Ming rides a bicycle from A to B. He starts to drive at a speed of 120 meters per minute, and then changes to a speed of 160 meters per minute. It takes him 1 hour to reach B. How many meters away did Xiao Ming change his speed from A?
AB两地相距8千米，小明骑自行车从A地去B地，开始以每分钟120米的速度行驶，后来改为每分钟160米的速度行驶，共用了1小时到达B地．小明是在离A地多少米的地方改变速度的？
<gadget id="calculator">120 * 60</gadget>
<output>7_200</output>

<gadget id="calculator">8_000 - 7_200</gadget>
<output>800</output>

<gadget id="calculator">160 - 120</gadget>
<output>40</output>

<gadget id="calculator">800 / 40</gadget>
<output>20</output>

<gadget id="calculator">60 - 20</gadget>
<output>40</output>

<gadget id="calculator">120 * 40</gadget>
<output>4_800</output>

<result>4_800</result>