The switch in the circuit shown below has been closed for a long time before it is opened at
t = 0. Find the current $i(t)$ through the inductor for $t \ge 0$. Assume $R_1 = 2 \text{ k}\Omega$, $R_2 = 1 \text{ k}\Omega$, $R_3 = 15$
$\text{k}\Omega$, $I_s = 3 \text{ mA}$, $L = 200 \text{ mH}$.