In a batch drying experiment, a solid with a critical moisture content of $0.2 \: kg$ $H_2O/kg$ dry solid is dried from an initial moisture content of $0.35 \: kg$ $H_2O/kg$ dry solid to a final moisture content of $0.1 \: kg \: H_2O/kg$ dry solid in $5 \: h$. In the constant rate regime, the rate of drying is $2 \: kg \: H_2O/(m^2.h)$.

The entire falling rate regime is assumed to be uniformly linear. The equilibrium moisture content is assumed to be zero.

The mass of the dry solid per unit area is _______ $kg/m^2$ (round off to nearest integer).