Y是水流速度吗?
航行了：2(X+Y)+3(X-Y)=(5X-Y)千米,
2/(X+5)=3/(X-5)-35
2(X-5)=3(X+5)-35(X^2-25),
35X^2-25X-900=0
7X^2-5X-180=0
X≈(5±71)/14,
X=38.