A man rows at 6 km/h in still water, and the river flows at 2 km/h. It takes him 3 hours to row to a place and back. How far is the place?

Explanation

1. 01

   Downstream he makes 8 km/h, upstream 4 km/h. For a distance $d$: $\frac{d}{8} + \frac{d}{4} = 3$.

2. 02

   $\frac{3d}{8} = 3$, so $d = 8$ km.