For $t>0$, find the Norton equivalent network seen by the inductor in Figure P4.28. Use that result to determine the associated time constant. Assume:
$$
\begin{array}{ll}
V_1=12 \mathrm{~V} & V_2=5 \mathrm{~V} \\
L=3 \mathrm{H} & R_3=R_2=2 \Omega \\
R_3=4 \Omega &
\end{array}
$$
(FIGURE CAN'T COPY)
Figure P4.28