A porous sotid under constant drying conditions takes $6$ hours to reduce the moishre content from $27$ to $9\%.$ The critical moishere content is $14\%$ and the equilibrium moishure content is $2\%.$ If the rate of dyying $m_0$ the falling rate period is proposition to the free moishure antiont, how long will if take to dry the sample of the same sotid from $35$ to $5\%$