Find $I_o$ in the network shown given that $V_1 = 2 V, V_2 = 10 V, I_1 = 3 mA, R_1 = 10 k\Omega, R_2 = 12 k\Omega,$ $R_3 = 7 k\Omega$ and $R_4 = 3 k\Omega.$

$I_o =$ $mA$