Answer
$v=16.0m/s$
Work Step by Step
We know that
$ v= v_0 + at$
Where $v$ is velocity at $ t= 4s $, $v_0$ is intial velocity, and $at$ is area under acceleration-time graph.
$\therefore v= 8.0m/s + 1/2×4m/s²×4.0s$
$v= 8.0m/s + 8.0m/s$
$v= 16.0m/s$
