Using Thévenin to find I3 current

i'm an engineering student and i've come across this problem i have to use Thévenin method, even though i could find Zth by "short circuiting" the power sources and opening the circuit at I3, i'm really having trouble to find Vth, and i need help with this problem. How can i manage to find Vth and the I3(load) current?

• Thevenin voltage is basically the voltage across where you define your load, which can be different depending on where you want your load to be. This is where you need to specify where your load is. – KingDuken Dec 1 '19 at 3:37
• Just a simplifying suggestion. Swap the positions of $E_2$ and your $15\:\Omega$ resistor and then treat the bottom wire as $0\:\text{V}$ (or ground.) It gets a lot easier to understand, then. And it's no different than what you have for analysis purposes. – jonk Dec 1 '19 at 5:12