Find $I_0$ in the network using Norton's theorem 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, $R_N$ = $k\Omega$

The Norton current (pointing down) obtained when replacing $R_2$ by a wire, $I_{N} =$ $mA$

$I_{o} =$ $mA$