7、A river flows at a uniform speed, with docks A and B located upstream and downstream, respectively, 200 kilometers apart. Boats A and B depart from docks A and B simultaneously and head towards each other. After meeting, they continue to their respective destinations, immediately turn around, and meet again on their return journey. If the interval between the two meetings is 4 hours, and the still water speeds of boats A and B are $36 \mathrm{~km} / \mathrm{h}$ and $64 \mathrm{~km} / \mathrm{h}$, respectively, then the speed of the current is $\qquad$ $\mathrm{km} / \mathrm{h}$
【Answer】 14
【Analysis】 In the context of boats moving in a stream, the time of meeting is independent of the water speed. The first meeting takes $200 \div$ $(36+64)=2$ (hours), and the second meeting takes $2+4=6$ (hours). Together, they cover 3 full distances, which takes $2 \times 3=6$ (hours), which is exactly the same. This indicates that both boats turn around at the same time. Therefore, the downstream speed of $\mathrm{A}$ equals the upstream speed of $B$: $(64-36) \div 2=14(\mathrm{~km} / \mathrm{h})$