There are two wharfs A and B on a river. Wharf A is 50 kilometers upstream of Wharf B. A passenger ship and a cargo ship depart from both Wharfs A and B simultaneously and travel upstream. The speed of the two ships in still water is the same. The passenger ship When starting out, an object falls into the water from the boat. After 10 minutes, the object is 5 kilometers away from the passenger ship. After traveling 20 kilometers, the passenger ship turns around and catches up with the object. When catching up, it happens to meet the cargo ship. Find the speed of the water flow.
一条河上有甲、乙两个码头，甲码头在乙码头的上游50千米处，一艘客船和一艘货船分别从甲、乙两码头同时出发向上游行驶，两船的静水速度相同，客船出发时有一物品从船上落入水中，10分钟后此物品距客船5千米，客船在行驶20千米后掉头追赶此物品，追上时恰好和货船相遇，求水流的速度．
<gadget id="calculator">1 / 6</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">5 / (1/6)</gadget>
<output>30</output>

<gadget id="calculator">50 / 30</gadget>
<output>5/3 = around 1.666667</output>

<gadget id="calculator">30 * 2</gadget>
<output>60</output>

<gadget id="calculator">50 / 60</gadget>
<output>5/6 = around 0.833333</output>

<gadget id="calculator">(5/3) - (5/6)</gadget>
<output>5/6 = around 0.833333</output>

<gadget id="calculator">20 / (5/6)</gadget>
<output>24</output>

<gadget id="calculator">30 - 24</gadget>
<output>6</output>

<result>6</result>