A wet solid containing $20\%$ $\text{(w/w)}$ moisture (based on mass of bone-dry solid) is dried in a tray-dryer. The critical moisture content of the solid is $10\%$ $\text{(w/w)}$. The drying rate ($kg\:m^{-2}\: s^{-1}$) is constant for the first $4$ hours, and then decreases linearly to half the initial value in the next $1$ hour. At the end of $5$ hours of drying, the percentage moisture content of the solid is ____________ $\%$ $\text{(w/w)}$ (rounded off to one decimal place).