A Slab of Concrete and an Insulating Board Are in Thermal

Multiple Choice

A slab of concrete and an insulating board are in thermal contact with each other. The temperatures of their outer surfaces are 68°F and 50°F. Determine the rate of heat transfer (in BTU/ft²⋅h) if the R values are 1.93 and 8.7 ft²⋅°F⋅h/BTU, respectively.

A) 9.7
B) 2.5
C) 5.3
D) 1.7
E) 28