A Copper Sheet of Area Is Bonded to an Unknown

A copper sheet of area is bonded to an unknown metal sheet of area .The thickness of the unknown metal is half that of the copper.The outside surface of the copper sheet is held at a temperature of 80 ^$\circ$ C and the unknown metal sheet at 40 ^$\circ$ C.If the temperature of the copper-unknown metal interface is 60 ^$\circ$ C,what is the thermal conductivity of the unknown metal?

A) 386 W/(m*K)
B) 193 W/(m*K)
C) 258 W/(m*K)
D) 772 W/(m*K)
E) 220 W/(m*K)