assume the east-west direction along the x-axis such that east lies in positive x-direction and west lie in negative Y-direction.
In unit-vector notation , individual displacement can be represented as
A = displacement of car in east direction = 60 i
B = displacement of car in west direction = - 90 i
D = total displacement of the car
Total displacement of the car is given as
D = A + B
inserting the values
D = 60 i + (- 90 i)
D = - 30 i
negative sign indicates the direction in west
hence net displacement is 30 km in west direction