Final answer:
Acceleration is calculated by the change in velocity over time. Without the final velocity, a numerical answer can't be given, but the formula for acceleration, in this case, would be acceleration = v / 20 s, assuming 'v' is the final velocity in m/s towards west.
Step-by-step explanation:
If a car is parked and then, 20 seconds later, it is traveling at a certain speed going west, we can calculate its acceleration using the formula: acceleration = (final velocity - initial velocity) / time. Given that the car was initially at rest (initial velocity is 0 m/s) and the final velocity is not provided in the question, I will use a placeholder 'v' to represent the final velocity in meters per second (m/s). So, the acceleration would be 'v / 20 s' directed to the west. If west is considered the negative direction, this acceleration would be negative.
Since the car's velocity is increasing uniformly, this acceleration is constant. For example, an average acceleration of 8.33 m/s² west means the car's speed is increasing by 8.33 meters per second every second in the westward direction. A negative sign is usually used to denote the westward direction in this context. Please note, more information is required to provide the exact numerical acceleration for the car mentioned in your original question.