Q: Determine the voltage V_cf in the network.

Solution:  We have to determine the voltage V_cf in the network. The network might be redrawn like

            We can let two paths for determining voltage V_cf that are abcfa & cdefc.

                                    By applying KVL equation for the path abcfa

                                                -4 +9 - V_cf -6 =0

                                                                  V_cf = -1 volts ----------------- (1)

                                    By applying KVL equation cdefc will be

                                                5 + 6 - 12 + V_fc =0                                                                                                                               V_fc= 1Volts ---------------(2)

            In the above mention equation we contain Vfc rather than V_cf . But we need to calculate V_cf.

                                    Here   V_cf = -V_fc

                        Therefore from equation B we contain

                                           V_cf = -1Volts