heat transfer Questions

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: