3. Points $A, B, C$ are located sequentially, with the distance $A B$ being 3 km and the distance $B C$ being 4 km. A cyclist departed from point $A$ and headed to point $C$. At the same time, a pedestrian left point $B$ and headed to point $A$. It is known that the pedestrian and the cyclist arrived at points $A$ and $C$ simultaneously. Find the distance from point $A$ where they met.
Answer: 2.1 km.

Solution: The speeds of the cyclist and the pedestrian are in the ratio $7: 3$, the point of their meeting divides $A B$ in the same ratio.