Answer: 0.75 Km, north
Explanation:
By definition, displacement is the object overall change in position and it is a vector quantity. In simpler term, it is the measure of how far out of place an object is.
From the question, the Library is the starting point and can be termed point (0).
From point (0), Patricia moves in the north direction with roller skates and cover 0.5 Km. Then walks 0.25 Km in the same direction.
Therefore, Patricia's total displacement from point (0) is the change in distance between the starting point, Library, and the final destination, her friend's house.
That is, (0.5 km) north+ (0.25km) north
= 0.75 Km, north
