Calculate current in branch using Thévenin's theorem
This is how I would split up the circuit using Thévenin. Next step is calculating \$U_{Th1}\$, \$U_{Th2}\$, \$R_{Th1}\$, \$R_{Th2}\$ and drawing the resulting circuit. Then solving \$I_x\$ should be easy.







simulate this circuit &ndash; Schematic created using CircuitLab

As a response to your comment: Shuffle the symbols around a bit ... Nothing changed! You can change positions of components in series:







simulate this circuit