The volume charge density of a sphere of radius 6 m is $2 \mu \mathrm{C} \mathrm{cm}^{-3}$. The number of lines of force per unit surface area coming out from the surface of the sphere is $\_\_\_\_$ $\times 10^{10} \mathrm{NC}^{-1}$. [Given : Permittivity of vacuum $\in_0=8.85 \times 10^{-12} \mathrm{C}^2 \mathrm{~N}^{-1}-\mathrm{m}^{-2}$ ]