Final answer:
Acceleration is calculated by subtracting the initial velocity from the final velocity to find the change in velocity and dividing that by the change in time.
Step-by-step explanation:
To calculate acceleration, you must first determine the change in velocity and the change in time. Acceleration is defined as the change in velocity divided by the time over which this change occurs. Therefore, the correct way to calculate acceleration is to subtract the initial velocity from the final velocity to get the change in velocity, and then divide this value by the time interval during which the change occurred. The formula for average acceleration is expressed as (final velocity - initial velocity) / time, which corresponds to option 3 in the question.