It sounds like you're supposed to find the average velocity [tex]\bar v[/tex] over the total 3.8 seconds, which would be given by
[tex]\bar v=\dfrac{\Delta x}{\Delta t}=\dfrac{x-x_0}{t-t_0}[/tex]
where [tex]x[/tex] is the displacement at time [tex]t[/tex], [tex]x_0=0[/tex] is the initial displacement from the origin, and [tex]t_0=0[/tex] is the starting time. Then the average velocity over the total 3.8 seconds,
[tex]\bar v=\dfrac xt,[/tex]
is determined entirely by the displacement of the particle after 3.8 seconds, so that
[tex]\bar v=\dfrac{-9.23\,\mathrm m}{3.8\,\mathrm s}\approx-2.4\,\dfrac{\mathrm m}{\mathrm s}[/tex]
