If $2.5\times {10}^{-6} \mathrm{N}$ average force is exerted by a light wave on a non-reflecting surface of $30{ \mathrm{cm}}^2$ area during $40 \min$ of time span, the energy flux of light just before it falls on the surface is _______ $\mathrm{W} {\mathrm{cm}}^{-2}.$(Round off to the Nearest Integer), (Assume complete absorption and normal incidence conditions are there)