For each piecewise-defined function,
(a) calculate $f(-1), f(0), f(1)$, and $f(2)$, and (b) sketch a graph of $f$.
$$
f(x)=\left\{\begin{aligned}
4 x-1, & \text { if } x<0 \\
2, & \text { if } x=0 \\
-3 x+5, & \text { if } x>0
\end{aligned}\right.
$$