$8.$ A slab with a wet weight of $5$ kg originally $50\%$ moisture $($wet basis$).$ The slab is $600$ by $900$ by $75$ mm thick. The equilibrium moisture content is $5\%$ of the total weight when in contact with air of $20$C and $20\%$ humidity. The drying rate is given below for contact with air of the above quality at a definite velocity. Drying is from one face only. How long will it take to dry the slab to $15\%$ moisture content $($wet basis$).$

Wet slab weight, $($Kg$)$

$9\mathrm{.}1$

$4\mathrm{.}9$

$7\mathrm{.}2$

$4\mathrm{.}9$

$5\mathrm{.}3$

$4\mathrm{.}4$

$4\mathrm{.}2$

$3\mathrm{.}9$

$3\mathrm{.}3$

$2\mathrm{.}9$

$2\mathrm{.}7$

$3\mathrm{.}4$

$2\mathrm{.}0$

$1\mathrm{.}0$

Drying rate, $($Kg$/$mhr$)$