Materials A, B, and C Have R Values of 1 $\degree$

Multiple Choice

Materials A, B, and C have R values of 1, 4, and 8 ft2- $\degree$ F-hr/Btu, respectively. If the rate of heat transfer through material A alone is 20 Btu/hr, then the rate of heat transfer through the combination of A, B and C is _____.

A) 1.5
B) 2.5
C) 4.0
D) 7.0
E) 80 Btu/hr