In this circuit all the components that have values are known, values of components that aren't shown are considered unknown. If the switch is off, then current I1' is known and it's 100mA. Now, i'm not really sure how to find the value of the current I3 after the switch is closed. I tried to solve it and i did it this way:
1. While switch was off, I found Thevenin generator for the part of the circuit right from the R3, Rt was 50 Ohms and i could't find the value of Et
2. Now, Et and E3 were in series, so were the resistors, so i summed up values of resistances Rt and R3 and it was 200 Ohms, and placed one E instead of Et and E3 (considering E=E3+Et)
3. Since i have the value of Ig1 and I1' i found the current through the E and R3 resistor and it was 75mA
4. After that, i found the voltage R1*I1'-E1 because it was equal to I3*200-E1 so i could find E and it was 23V
5. When the switch turned on i wasn't considering original circuit, i used circuit with E=23V and R=200Ohms right from the branch with switch.
6. Using node voltage method i found out that I3=29mA (i considered I3 is current through R and E, but i'm not sure if that's correct because circuit looked different at the begging so i'm not sure is that the I3 i need to find)
1. While switch was off, I found Thevenin generator for the part of the circuit right from the R3, Rt was 50 Ohms and i could't find the value of Et
2. Now, Et and E3 were in series, so were the resistors, so i summed up values of resistances Rt and R3 and it was 200 Ohms, and placed one E instead of Et and E3 (considering E=E3+Et)
3. Since i have the value of Ig1 and I1' i found the current through the E and R3 resistor and it was 75mA
4. After that, i found the voltage R1*I1'-E1 because it was equal to I3*200-E1 so i could find E and it was 23V
5. When the switch turned on i wasn't considering original circuit, i used circuit with E=23V and R=200Ohms right from the branch with switch.
6. Using node voltage method i found out that I3=29mA (i considered I3 is current through R and E, but i'm not sure if that's correct because circuit looked different at the begging so i'm not sure is that the I3 i need to find)