A wall is constructed of a 2 inch layer of fiberglass board (R= 8) and six inches of fiberglass batting (R= 19). If the temperature on the outside surface of the fiberglass board is 50°F and the temperature on the inside surface of the fiberglass batting is 68°F, what is the temperature (in°F) at the interface? (The units ofRare ft2°F h/BTU.)