Determine V_o using superposition.

First, kill the 7 mA current source. I will use nodal analysis to find V_o7.

Define Dependent source parameter in terms of node voltages.

if = (V_A - V_B) / 5 K

35 volt source forms supernode (dotted purple outline) with reference node.

V_A = 35 V

KCL at node B:

20 (35 - V_B) + 4 (35 - V_B) - V_B = 0

25 V_B = 840

V_B = 33.6 V = V_o7 (Intermediate result 1)

Now replace the current source and kill the 35 V source. I will again use nodal analysis to find V_o35.

Define Dependent source parameter in terms of node voltages.

if = - V₁ / 5 K

KCL at node 1:

20 (- V₁) - 4 (V₁) - V₁ = 140

25 V₁ = - 140

V₁ = - 5.6 V = V_o35 (Intermediate result 2)

Finally

V_o = V_o7 + V_o35 = 33.6 - 5.6

V_o = 28 V