Superpostion theorem

I'm trying solve this scheme:



but not with the ideia of solve it but yes with the ideia of understand the dynamic of the thing...

aftwer watch this video:
https://www.youtube.com/watch?v=x4qdec6kH1Q

and read about the superposition:
http://en.wikipedia.org/wiki/Superposition_theorem

I did this scheme for solve the problem:



But, and now, how make the graphical superposition?

Attached Images

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