Calculate the required drying time in hours at a constant rate to dry apple slices from a moisture content of $80\%$ to $40\%$ at a constant drying rate $$ of $0\mathrm{.}75kg{H}_{2}O$ per kg dry matter per hour. State the results with $2$ decimal digits $($e$.$g$.,1\mathrm{.}11)$ without unit!