Apple slices $4mm$ thick are exposed to sulphur fumes from top in a sulphuring house before drying. If the Biot number for mass transfer is higher than $40,$ and the surface concentration of $S{O}_2$ is $0\mathrm{.}1mo\frac{l}{m}3,$ determine how long it will take for the concentration on the non$-$exposed surface of the apple slice to increase by $5\%$ of the initial concentration difference using both the analytical solution and Heisler charts. Assume zero initial concentration of $SO2$ in the apple, negligible mass transfer through the sides of the apples, and a diffusion coefficient of $SO2$ in the apple of $110-9m\frac{2}{s}.$