Find V_o

I will choose node d as the reference node and assign node voltages V_A, V_B, and V_C to nodes a, b, and c respectively. Thus the equations are:

Node A forms a supernode with the reference node due to the 75 V source (shown with a dotted outline):

V_A = 75

KCL at node B:

Simplify and collect terms

10 V_A - 10 V_B + 5 V_C - 5 V_B - 4 V_B = 0

10 (75) - 19 V_B + 5 V_C = 0

- 19 V_B + 5 V_C = - 750 (Eq. B)

KCL at node C:

Simplify and collect terms.

4800 + V_A - V_C + 20 V_B - 20 V_C - 4 V_C = 0

4800 + 75 + 20 V_B - 25V_C = 0

20 V_B - 25V_C = - 4875 (Eq. C)

Solving Equations B and C yields:

V_A = 75 V

V_B = 115 V

V_C = 287 V

Thus since V_o = V_B - V_A

V_o = 115 - 75
V_o = 40 Volts