Find current passing through resistor

[snabelpablo]

http://img5.imageshack.us/img5/6889/imagepf.jpg

I need to create a formula using R (resistance), U1 and U2 (voltage) for the current flowing through the 8 Ohm resistor. I've been looking at this for hours now and I still don't even know where to begin. Can anyone get me started on this?

 

[willem2]

Find the current in the circuit where U1 is shorted, and the current in the circuit where U2 is shorted and add them (watch the direction of the current)

if you short either one of the voltage sources, the rest of the network can be reduced with series and parallel resistances.

for an explanation see here

http://www.allaboutcircuits.com/vol_1/chpt_10/7.html

 

[Delphi51]

The resistor formula is V = IR.
There can only be one voltage across a resistor. It isn't clear what your U1 and U2 are - perhaps they are the voltages with respect to ground on the two ends of the resistor. If so, replace the V in the formula with U1 - U2.

 

[snabelpablo]

I must have missed something basic because I still can't wrap my brain around this.
Here is how I see it (and this is probably very wrong since I know next to nothing about this):

Current from the first power source with the voltage U1 can go through resistor 6+4 OR 6+R OR 8. If I put this into the formula R=(1/R1 + 1/R2 + ... + 1/Rn)^-1 i get the resultant resistance which will be an expression containing R. I do the same for the second power source that must go through 2 and the same parallell connection. I can then use I=V/R to find the current through the 8 Ohm resistor. Or can I?

Maybe someone could show me with some calculations?