The man first walks 6 km towards the West. He then turns and walks 3 km towards the South. The two directions in which the man walks are perpendicular to each other.
The distance between the final point and the initial point is given by `sqrt(6^2 + 3^2) = sqrt(36 + 9) = sqrt(45) = 3*sqrt 5`
The point at which the man reaches finally is at a distance of `3*sqrt 5` from his initial point.