The volume charge density of a sphere of radius 6 m is $2 \mathrm{\mu C}{ \mathrm{cm}}^{-3}$. 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 ${\in }_0=8.85\times {10}^{-12}{\mathrm{C}}^2{\mathrm{N}}^{-1}-{\mathrm{m}}^{-2}$ ]