How much heat (Btu's) will be stored in a 5 foot high by 20 foot long concrete wall 1 ft. thick if it is warmed from 65 deg. F to 85 deg. F by exposure to sunlight? O a) 15,600 BTU O b) 25,350 BTU O c) 35,500 BTU O d) 44,900 BTU Main Content O e) 55,000 BTU