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