Hi,
this is the task i'm trying to solve:
http://imageshack.us/photo/my-images/811/zwischenablage01dy.jpg/

my approach is this:
v = (I-1.5A)*20
I = 24V / (5+20||12)||8)

I'm not sure if this is correct.. please help me if i'm wrong

 

Are you familiar with solution by superposition? It is readily solved by that method.

 

it would be better if you post all the necessary steps. are you familiar with node and mesh analysis?

 

superposition is a good way to do it. check out this example :

http://www.wisc-online.com/objects/ViewObject.aspx?ID=DCE3802

it doesn't have a current source, but the approach is the same. It goes through all the steps. The key is, in the end, to keep track of polarity.

 

so, would you say my approach is correct?

 

No your method is incorrect. It would be helpful if you redraw the schematic with the assumed unknown currents & voltages. Then present your equations in the context of the schematic.