Two parallel rail tracks run north-south. Train \(A\) moves north with a speed of \(54\text{ km/h},\) and train \(B\) moves south with a speed of \(90\text{ km/h}.\) The magnitude of the velocity of \(B\) with respect to \(A\) is:
1. \(40\text{ m/s}\)
2. \(0\text{ m/s}\)
3. \(25\text{ m/s}\)
4. \(15\text{ m/s}\)