There are two small boats A and B. Their speeds in still water are 10 km/h and 6 km/h respectively. The distance between the upstream and downstream of a river is 48 km. The small boat A goes upstream from the downstream, and the small boat B Going downstream from the upper reaches, the two boats set off at the same time. After meeting on the way, after another 2 hours, the boat A reaches the upper reaches. What is the velocity of the water in km/h?
有两艘小船A、B，它们在静水中的航行速度分别是10千米/时和6千米/时，一条河流的上游和下游相距48千米，小船A从下游逆流而上，小船B从上游顺流而下，两船同时出发，在途中相遇后，再过2小时，A船到达上游．则水流速度是多少千米/时．
<gadget id="calculator">10 + 6</gadget>
<output>16</output>

<gadget id="calculator">48 / 16</gadget>
<output>3</output>

<gadget id="calculator">3 + 2</gadget>
<output>5</output>

<gadget id="calculator">48 / 5</gadget>
<output>48/5 = around 9.6</output>

<gadget id="calculator">10 - (48/5)</gadget>
<output>2/5 = around 0.4</output>

<result>2/5 = around 0.4</result>