Final answer:
The correct statement for a car slowing down as it travels east is that its acceleration is in the -x direction because it is decelerating, with acceleration opposite to motion.
Step-by-step explanation:
When a car traveling to the east (in the +x direction) begins to slow down as it approaches a traffic light, its acceleration must be in the -x direction. This is because the car is decelerating, or slowing down, which means that the direction of its acceleration is opposite to its direction of motion. Thus, the correct statement concerning its acceleration is that it is in the -x direction. Decreasing speed while moving in the positive direction indicates that the acceleration is negative.