1. Understand the Formula:

* Acceleration (a) = (Final Velocity (vf) - Initial Velocity (vi)) / Time (t)

2. Identify the Values:

* Initial Velocity (vi) = 5 miles per second

* Final Velocity (vf) = 20 miles per second

* Time (t) = 3 seconds

3. Plug the Values into the Formula:

* a = (20 miles/second - 5 miles/second) / 3 seconds

* a = 15 miles/second / 3 seconds

* a = 5 miles/second²

Answer: The acceleration is 5 miles per second².