Use nodal analysis to find $V_o$ in the network shown given that $V_1 = 3 V, I_1 = 7 mA, R_1 = 2 k\Omega,$ $R_2 = 5 k\Omega, R_3 = 6 k\Omega$ and $R_4 = 4 k\Omega.$

$V_o =$ $V$