A Wall Is Constructed of a 5 Cm Layer of Fibro

Multiple Choice

A wall is constructed of a 5 cm layer of fibro board (R = 1) and 15 cm of fibreglass batting (R = 3) . If the temperature on the outside surface of the fibreglass board is 40 $\degree$ C and the temperature on the inside surface of the fibreglass batting is 20 $\degree$ C, what is the temperature (in $\degree$ C) at the interface?

A) 25
B) 30
C) 35
D) 33.3
E) 36.6