The answer is 20V but I am having problems figuring out how it is derived. I think there is a supernode in there but the voltage sources in parallel have got me confused.

 

KCL(Vo):

\(\frac{Vo - 30}{2k} + \frac{Vo - 20}{5k} + \frac{Vo}{4k} = 0\)

\(Vo(\frac{1}{2} + \frac{1}{5} + \frac{1}{4}) = 19\)

\(Vo(\frac{20 + 8 + 10}{40}) = 19\)

\(Vo(\frac{38}{40}) = 19\)

\(Vo = 20\)