Q:  Determine the value of voltage V_ac .

 Solution: We need to determine the voltage V_ac. To solve out this problem the circuit might be redrawn like

            Let the current I₁ is passing through the circuit. The KVL equation will be like

                                                10kI₁ + 20kI₁ + 30KI₁ -6 = 0      

                                        10kI₁ + 20kI₁ + 30KI₁ = 6

                                                                               60kI₁= 6

                                                                      I₁ = 6/60k

                                                                               I₁ = 0.1mA

                                    Now Vac will be equivalent to

                                                V_ac = (10k + 20k)I₁

                                                       =   30k(0.1mA)

                                                V_ac =   3 V