Q:   Determine the value of voltage V_ac .

Solution:    We need to calculate the voltage V_bd. First we will need to calculate the voltage across 40k resistor.             Consider the current I₁  be passing through the loop.

                                    Applying KVL for loop

                                                10kI₁ + 9 + 40kI₁+ 10kI₁ - 6 = 0

                                                                                         60kI₁ = -3

                                                                                    I₁ = - 3/60k= - 0.05 mA

                                    therefore, voltage across 40kΩ resistor

                                                                                          V_40k = (-0.05m)(40k)

                                                                                           = - 2 V  ---------- (1)

                        We need to want to calculate V_bd we can redraw the circuit like

                        Now to determine V_bd we take the loop bdcb

                         Applying KVL to the loop

                                                             V_bd - V_40k  -9 =0 

                         Put the value of V_40k from equation (1) we obtain

                                                       V_bd - (-2) -- 9 =0   

                                                            V_bd +2 -9 =0   

                                                         V_bd = 7 V