A liquid column of height $0.04 \mathrm{~cm}$ balances excess pressure of a soap bubble of certain radius. If density of liquid is $8 \times 10^3 \mathrm{~kg} \mathrm{~m}^{-3}$ and surface tension of soap solution is $0.28 \mathrm{~Nm}^{-1}$, then diameter of the soap bubble is $\underline{\hspace{2cm}}\mathrm{cm}$. (if $\mathrm{g}=10 \mathrm{~m} \mathrm{~s}^{-2}$ )