The total length of the Yangtze River is about 6300 kilometers, the length of its downstream accounts for about 1/7 of the total length, and the length of its upper reaches (1/5). How many kilometers is the length of the upper reaches of the Yangtze River?
长江全长约6300千米，其下游的长度约占全长的(1/7)，约是上游的(1/5)，长江上游的长度大约是多少千米？
<gadget id="calculator">1 / 7</gadget>
<output>1/7 = around 0.142857</output>

<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/7) / (1/5)</gadget>
<output>5/7 = around 0.714286</output>

<gadget id="calculator">6_300 * (5/7)</gadget>
<output>4_500</output>

<result>4_500</result>