A cup of coffee cools from 90^° C to 80^° C in t minutes, when the room temperature is 20^° C. The time taken by a similar cup of coffee to cool from…

A cup of coffee cools from $\displaystyle 90^{\circ} \mathrm{C}$ to $\displaystyle 80^{\circ} \mathrm{C}$ in $\displaystyle t$ minutes, when the room temperature is $\displaystyle 20^{\circ} \mathrm{C}$. The time taken by a similar cup of coffee to cool from $\displaystyle 80^{\circ} \mathrm{C}$ to $\displaystyle 60$°C at a room temperature same at $\displaystyle 20$°C is :