If the average velocity of the duck is zero, it means that the duck's location at the end of the time interval was the same as at the beginning of the interval, but says nothing about the duck's motion during that time. For instance, the duck could have waddled around in a circle 20 times; as long as it wound up at the starting point, the displacement and average velocity is zero.
Then, the velocity of the car is decreased by half: so, the new kinetic energy is So, the new kinetic energy is 1/4 of the initial kinetic energy of the car. Numerically: