Car A and car B are both traveling down a straight highway at 90 km/h. Car A is only 6.0 meters behind car B. The driver of car B brakes, slowing down with a constant deceleration of 2.0 m/s². After 1.2 seconds, the driver of car A begins to brake, also at 2.0 m/s², but this is insufficient and the cars eventually collide, both still moving forward. What is the relative velocity of the two cars at the moment of the collision?
a) 2.4 m/s
b) 5.0 m/s
c) 9.5 m/s
d) 21 m/s
e) 24 m/s