The velocity of an object is a vector quantity. It has both magnitudes as well as direction.
Arrows are used to show direction.
Car A is moving towards west. Car B is moving towards east-south direction. Car C is moving towards South direction. Car E is moving towards North direction.
So, the correct option is (a) i.e. Car A has a velocity of 40 km/hr west.
Is the car is moving in a constant direction with constant speed, the composite force is null. We know what because any object that nonzero composite force is applied to will accelerate in the direction of the force, and this one doesn't.