When you see a traffic light turn red, you apply the brakes until you come to a stop. if your initial speed was 12 m/s, and you were heading due west, what was your average velocity during breaking? assume constant deceleration.

The final velocity of the decelerating car should be 0 m/s. The average velocity is obtained by dividing by two the sum of initial and final velocities. 
                          Vave = (Vi + Vf) / 2
Substituting the values,
                             Vave =  (12 m/s + 0 m/s) / 2
Thus, the value of the average velocity is 6 m/s.