From the question we come to know several important information's and based on them we can reach the desired result.
Initial speed = 0 m/s
Final speed = 10 m/s
Initial time = 0 sec
Final time = 4 sec
Then
Average acceleration = (Final speed - Initial speed)/(Final time - Initial time)
= (10 - 0)/(4 - 0)
= 10/4
= 2.5 m/s^2
So the average acceleration is 2.5 m/s^2. I hope this has made it clear to you about the procedure of solving such problems.
