Q:  Compute the value of current I using source transformation method.

Solution:          we have to calculate the current I by using source transformation method.

3 Ohms resistor is in parallel to 5A source. therefore it can be transformed into a voltage source 15V.

3 Ohms resistor & 4 Ohms are in series and the resultant will in series to 15V therefore it can be transformed into a current Source.

                                    7|| 7 = 7 x 7 / 7+ 7 =49/14 = 3.5 ohm

Current source is in parallel to 3.5 ohms resistance. Therefore it can be modified into a Voltage source by Ohm's Law

                                                V =IR= 15/7 X 3.5 = 7.5 V

            The current I can be determined using KVL

                                     -7.5 + 3.5I - 51Vx  + 28I +9 =0 -------------- (i)

                                    Here   V_x = 2I

                                    Put the value of Vx in (i) we get

                                    -7.5 + 3.5 I - 51(2I) + 28I +9 = 0

                                                 3.5I -102I +28I + 1.5 = 0

                                                                 -70.5I +1.5 = 0

                                                                        I = 1.5/70.5

                                                                                I = 21.28mA          Ans.