To calculate Stanley's acceleration, we can use the formula:
acceleration = (change in velocity) / (time taken)
The change in velocity is the final velocity minus the initial velocity, which is 11 m/s - 3.5 m/s = 7.5 m/s.
Given that the time taken is 3 seconds, we can now calculate the acceleration:
acceleration = 7.5 m/s / 3 s = 2.5 m/s^2
Therefore, Stanley's acceleration is 2.5 m/s^2.