If the potential at A is 2000V the potential at B is 

The circuit can be reduced as

As the capacitors, 5$\mu F$ and 15$\mu F$ are in series, so potential across 5 is

${\mathrm{V}}_{\mathrm{A}}-{\mathrm{V}}_{\mathrm{B}}=\frac{{\mathrm{C}}_{BC}}{{\mathrm{C}}_{AB}+{\mathrm{C}}_{BC}}\left({\mathrm{V}}_{\mathrm{A}}-{\mathrm{V}}_{\mathrm{C}}\right)$

$\Rightarrow 2000-{\mathrm{V}}_{\mathrm{B}}=\left(\frac{15}{5+15}\right)(2000-0)$

$$\begin{gathered} \Rightarrow 2000-V_B=1500 \\ \Rightarrow V_B=2000-1500=500\mathrm{V} \end{gathered}$$