Answer:
4m /s.
Step-by-step explanation:
Acceleration is defined as the change of velocity, that is, when the velocity increases or decreases, there's acceleration. When the velocity doesn't change, there's no acceleration or it's null.
So, in this case, the initial velocity of the accelerated period is 4m/s, and after the period is 60m/s. This means 4m/s represents the velocity before the acceleration and 60m/s represents the velocity after the acceleration.
Therefore, the right answer here is 4m/s.