Find $V_o$ in the circuit shown given that $V_{S1} = 7 V$, $V_{S2} = 11 V$, $I_{S1} = 2 A$, $R_1 = 8 \Omega$, $R_2 = 10 \Omega$, $R_3 = 6 \Omega$, $R_4 = 3 \Omega$,and $R_5 = 8 \Omega$.

The best choice for the reference node is the middle node, since that node has the most elements connected to it and it has one terminal of both voltage sources connected to it.
Use the convention from Hayt, Kemmerly and Durbin that currents enter the node from current sources and leave the node through resistors.

The nodal analysis equation at node 1:
$V_1$ + $V_2$ + $V_3$ + $V_4$ =

The nodal analysis equation at node 2:
$V_1$ + $V_2$ + $V_3$ + $V_4$ =

The nodal analysis equation at node 3:
$V_1$ + $V_2$ + $V_3$ + $V_4$ =

The nodal analysis equation at node 4:
$V_1$ + $V_2$ + $V_3$ + $V_4$ =

$V_1=$ $V$
$V_2=$ $V$
$V_3=$ $V$
$V_4=$ $V$
$V_o=$ $V$