The opposite faces of a metal slab of thickness $5 \mathrm{~cm}$ and thermal conductivity $400 \mathrm{~W} \mathrm{~m}^{-1}{ }^{\circ} \mathrm{C}^{-1}$ are maintained at $500{ }^{\circ} \mathrm{C}$ and $200{ }^{\circ} \mathrm{C}$. The area of each face is $0.02 \mathrm{~m}^{2}$. Assume that the heat transfer is steady and occurs only in the direction perpendicular to the faces. The magnitude of the heat transfer rate, in $\mathrm{kW}$, rounded off to the nearest integer, is $\_\_\_\_\_\_\_\_$.