Hi there! :)
[tex]\large\boxed{v_{f} = 18 m/s}[/tex]
Use the following kinematic equation to solve for the final velocity:
[tex]v_{f} = v_{i} + at[/tex]
In this instance, the runner started from rest, so the initial velocity is 0 m/s. We can rewrite the equation as:
[tex]v_{f} = at[/tex]
Plug in the given acceleration and time:
[tex]v_{f} = 4.5 * 4 = 18 m/s[/tex]
