Acceleration is defined as the velocity of an object over a period of time.
Mathematically,
Acceleration, A = Velocity [V] /Time [T]
From the question given above, we are told that
T = 30 seconds
Initial velocity, V1 = 5
Final velocity, V2 = 2
Change in velocity, V = V1 - V2 = 5 - 2 =3
A = V / T = 3 / 30 = 0.1
Therefore A = 0.1 m/s^2.