A Wall Assembly (Total Area = 100 Ft2)consists of 80

Multiple Choice

A wall assembly (total area = 100 ft2) consists of 80 ft2 of opaque wall with an R- value of R- 20 and a 20 ft2 of window whose R- value is R- 2. The effective (overall) R- value of the entire wall assembly is approximately

A) R- 15.
B) R- 7.
C) R- 11.
D) R- 3.
E) none of the above.