Given data
*A person walks from home to store in north direction is d_1 = 200 m
*Then, he travels from store to friend's house in south direction is d_2 = 600 m
The formula for the total displacement is given as

Substitute the known values in the above expression as

Here, the negative sign indicates that the person is moving in the south direction.
Hence, the total displacement is -400.0 m