## Essential University Physics: Volume 1 (4th Edition)

$R-factor = 25 \frac{^{\circ} F ft^2 h}{Btu}$
We find: $R-factor= \frac{ \Delta T}{ H}$ We plug in the given values: $R-factor = \frac{1}{.040}$ We find: $R-factor = 25 \frac{^{\circ} F ft^2 h}{Btu}$