If the velocity of an object changes from 65 m/s to 98 m/s during a time interval of 12 s what is the accerlation of the object

Acceleration is the derivative of velocity, meaning it represents the change in velocity for a given time interval. So while velocity is in m/s, we know that acceleration is m/s per s, meaning m/s^2. Acceleration is given by the change in velocity (m/s) divided by the time elapsed (per s), so a = (98-65)/12.