Thevenin and Norton circuit analysis example
This is easy to solve:



You keep combining sources until you are left with a single source.  In this case, working with Thevenin sources (as apposed to Norton) seems easier.

V1,R1 is a Thevenin source you can see by inspection.  So is V2,R2.  Combine them.

Now add R3 to the resistance of that source.  That is the Thevenin equivalent looking left into the right side of R3.

Add R4 to this and force I4 thru the result.