The answer to this question would be: 1m/s
When you are walking to the north with 2m/s velocity, the stationary object(velocity=0m/s) will look like moving south at 2m/s velocity. That happens because the relative distance between you and the object is reduced by 2m/s in both conditions. In this question, the man seems like have 3m/s velocity. The real velocity should be:
3m/s - 2m/s = 1m/s