(a) Calculate the R value for a wall consisting of the following layers: concrete block (R = 1.93), 1.0 inch of insulating board (R = 4.3), and 0.50 inch of drywall (R = 0.45), all in U.S. Customary Units. 

(b) If the wall has an area of 15 m², find the heat flow per hour through it when the temperature just outside is 20 °C lower than inside.