Use Norton's theorem to find $V_0$ in the network given that $V_1 = 5 V, I_1 = 4 mA, R_1 = 4 k\Omega, R_2 = 10 k\Omega, R_3 = 12 k\Omega$ and $R_4 = 8 k\Omega$.

The Norton resistance at the terminals of $R_3$ with $R_3$ removed from the circuit:
$R_{N} =$ $k\Omega$
The short-circuit current resulting from removing $R_3$ and replacing by a short circuit:
$I_{N} =$ $mA$
$V_{o} =$ $V$