The energy stored in the capacitor in the steady state is

At steady state, capacitor acts as open circuit.

$\begin{array}{l}{\mathrm{V}}_{\mathrm{A}}+3\times 1-14-5\times 3={\mathrm{V}}_{\mathrm{B}}\\ \Rightarrow {\mathrm{V}}_{\mathrm{A}}-{\mathrm{V}}_{\mathrm{B}}=26\mathrm{V}\end{array}$

Energy stored in capacitor,

$\mathrm{U}=\frac{1}{2}{\mathrm{CV}}^2=\frac{1}{2}\times {10}^{-6}\times {\left(26\right)}^2=338\mathrm{\mu J}$