I got VR5=10V with the negative side on the top of R5. I have a page and a bit of handwritten working if you want to see it, but the general process was:
1. Define polarities of resistors (even if they're wrong, they just need to be logically consistent), ie R2 and R3 have their negative side on the node that connects to the left of the current source, and R5 R4 R3 and R1 have their positive side on the node that connects to the right side of the current source. (You can determine that by the direction of the current source)
2. By using KVL and defining your voltage loops, you can reduce the unknown voltages across resistors to 3. Ie Vr5=Vr4=Vr1, Vr5-Vr3+Vr2=0
3. Define your 3 KCL equations/nodes. There's one to the left of the current source, one to the right, then there's the node at the top.
4. Express each current quantity as a V/R quantity (ohms law). eg I5=Vr5/12000, I4=Vr5/6000 (remember Vr5=Vr4=Vr1)
5. Substitute the V/R values into your KCL equations.
6. Then by simplifying and substituting through the 3 KCL equations you can find the value of VR5. Compare that value against the assumed polarities of the resistors, eg VR5=10V, but remembering that the negative side is at the top.