A cup of coffee cools from `` 90^{\circ} C `` to `` 80^{\circ} C `` in t minutes, when the room temperature is `` 20^{\circ} C `` . The time taken by a similar cup of coffee to cool from `` 80^{\circ} C `` to `` 60^{\circ} C `` at a room temperature same at `` 20^{\circ} C `` is :
(A) `` \frac{13}{10} t ``
(B) `` \frac{13}{5} t ``
(C) `` \frac{10}{13} t ``
(D) `` \frac{5}{13} t ``