A body cools from 80^° C to 60^° C in 5 minutes. The temperature of the surrounding is 20^° C. The time it takes to cool from 60^° C to 40^° C is:

A body cools from $\displaystyle 80^{\circ} \mathrm{C}$ to $\displaystyle 60^{\circ} \mathrm{C}$ in $\displaystyle 5$ minutes. The temperature of the surrounding is $\displaystyle 20^{\circ} \mathrm{C}$. The time it takes to cool from $\displaystyle 60^{\circ} \mathrm{C}$ to $\displaystyle 40^{\circ} \mathrm{C}$ is: