Q$3$: A wet solid is to be dried in a tray dryer under steady state conditions from a free moisture content of $x_1=0\mathrm{.}4kg{H}_2\frac{O}{k}g$ dry solid to $x_2=0\mathrm{.}02kg{H}_2\frac{O}{k}g$ dry solid. The dry solid weight is $99\mathrm{.}8kg$ dry solid and the top surface area for drying is $4\mathrm{.}645m^2.$ the drying rate curve can be represented by Figure below.

a$-$ Calculate the time for drying using graphical integration in the falling rate period.

b$-$ Repeat but use a straight line through the organic for the drying rate in the falling rate period.