Chapter 5.5, Problem 20P

In each of Problems $19$ through $21$, find the Laplace transform of the given function:

$f\left(t\right)=\{\begin{array}{l}1,0\le t<1\\ 0,1\le t<2\\ 1,2\le t<3\\ 0,t\ge 3\end{array}$.