The P.D between the points A and B is

PD across 2C,C,2C chain inAB path also 60V.
Charge is same on each capacitor in that chain.
So, ${\mathrm{V}}_1:{\mathrm{V}}_2:{\mathrm{V}}_3=\frac{1}{{\mathrm{C}}_1}:\frac{1}{{\mathrm{C}}_2}:\frac{1}{{\mathrm{C}}_3}$
$\begin{array}{l}=\frac{1}{2}:\frac{1}{1}:\frac{1}{2}=1:2:1;\mathrm{V}={\mathrm{V}}_1+{\mathrm{V}}_2+{\mathrm{V}}_3=60\mathrm{V}\\ {\mathrm{V}}_2=\frac{60}{4}\times 2=30\mathrm{V}\end{array}$