On a winter’s day the outside temperature of a 17-in thick concrete wall is −29°F, the wall is 15 ft long and 9 ft high. How many BTUs are required to keep the inside of the wall at 69°? Assume the...

On a winter’s day the outside temperature of a 17-in thick concrete wall is −29°F, the wall is 15 ft long and 9 ft high. How many BTUs are required to keep the inside of the wall at 69°? Assume the thermal conductivity of the wall is 0.8 BTU/h ft°F.