Answer
$$v=8.0 \mathrm{\ m} / \mathrm{s} $$
Work Step by Step
the velocity is the integral of $F / m,$ so we find the "area" in the graph $(15$ units) and divide by the mass $(3)$ to obtain
$$v-v_{0}=15 / 3=5 $$
since
$$v_{0}=3.0 \mathrm{\ m} / \mathrm{s},$$
then
$$v=8.0 \mathrm{\ m} / \mathrm{s} $$
