Distance = 27m
Displacement = 3 metres South
Distance is a scalar quantity and it represents the length of the path taken by a body.
Displacement is a vector quantity and it represents the distance between the start and end points of a body.
Now to the question:
The car drives 12 metres North i.e
North (+ve)
∧
|
| 12m
|
|
The car then drives 15 metres South i.e
|
|
|
| 15m
|
∨
South (-ve)
(a) The car's distance d, is just the total distance covered to drive North and then South. i.e
d = 12m + 15m = 27m
(b) The car's displacement D, however takes into respect, the direction of the car as it drives to and fro.
Let North be taken as positive direction
Let South be taken as negative direction.
This means that;
12 m North = +12 m
15 m South = -15m
Therefore;
D = +12 - 15
D = -3m
Since the displacement is negative, then it means that the direction of the total displacement is South.
Therefore, the displacement is 3 metres South
PS: The arrow diagram has also been attached to this response