Calculate the total drying time $($in hr$)$ necessary to dry a product from $\%90$ to $25\%$ moisture $($wet basis$)$ in an industrial dryer where $2$ kg dry solids$/$m surface area exposed to the air is looded. It is given that the critical moisture content is $5$ kg water$/$ kg dry solids and the drying rate at constant drying period $($Rc$)$ is $3$kg water$/$m$.$h under the specified drying conditions. Assume the drying time for falling rate drying is $9$ hr$.$

a$)12\mathrm{.}66$ b$)15\mathrm{.}32$ c$)17\mathrm{.}98$ d$)11\mathrm{.}66$ e$)14\mathrm{.}77$