Find the 3 node voltages in the figure
You should get into the practice of re-drawing schematics:



simulate this circuit &ndash; Schematic created using CircuitLab
This way at least the components are labeled. But also notice that there is no need to indicate where \$I_1\$ sources because the voltage drop across it is already determined by the voltage at \$V_1\$. The above schematic is slightly simpler to read.
Obviously, \$I_x=\frac{V_2}{R_4}\$. And at this point you should be able to use KCL to set up three equations in three unknowns and solve.