A Copper Sheet of Area Is Bonded to an Aluminum

A copper sheet of area is bonded to an aluminum sheet of area .Both sheets have the same thickness.The outside surface of the copper sheet is held at a temperature of 80 ^$\circ$ C and the aluminum sheet at 40 ^$\circ$ C.What is the temperature of the copper-aluminum interface?

A) 48 ^$\circ$ C
B) 65 ^$\circ$ C
C) 70 ^$\circ$ C
D) 52 ^$\circ$ C
E) 60 ^$\circ$ C