The acceleration, $a$, of a particle is given by
$$
a=5-3 t
$$
Given that the initial displacement at $t=0$ is $-2.1 \mathrm{~m}$ and the initial velocity is $8 \mathrm{~m} / \mathrm{s}$, find expressions for the velocity and displacement.
[Hint: We have, $a=\frac{\mathrm{d} v}{\mathrm{~d} t}, v=\frac{\mathrm{d} s}{\mathrm{~d} t}$ where $s$ is the displacement