Answer;
= 4 km/hr
Step-by-step explanation;
All the motion is directed westward, so we can consider west to be positive.
The velocity of the first car relative to the second car is;
Vr = V1 - V2
= 71 km/hr - 67 km/hr
= 4 km/hr
The magnitude of the velocity of the first car relative to the second car is 4 km/hr.