How much time does it take a person to walk 12 km north at a velocity of 6.5 km/h

"6.5 km/hr" is not a velocity. It's just a speed, so

we don't know what direction he's walking.

If he happens to be walking north, then it takes him

(12 km) / (6.5 km/hr) = 1.846 ... hours (rounded).

If he's walking in any other direction, it takes him longer than that.

If the angle between north and the direction he's walking is

90 degrees or more, then he can never cover any northward

distance, no matter how long he walks. This is the answer