In each of problems 5 and 7, express the function $f(t)$ in terms of the unit step functions $u_c(t)$.
5. $f(t) = \begin{cases} 0, & 0 \le t < 3 \\ -2, & 3 \le t < 5 \\ 2, & 5 \le t < 7 \\ 1, & t \ge 7 \end{cases}$
7. $f(t) = \begin{cases} 1, & 0 \le t < 2 \\ e^{-(t-2)}, & t \ge 2 \end{cases}$