A batch dryer with a grain depth of 20 inches contain 21,000 pounds of 20.7% (wb) moisturecontent shelled corn. An airflow of 75,000 pounds dry air per hour is supplied at a temperature of 175°F. The ambient air is 55°F at 100% relative humidity. The grain is dried to an average moisture content of 13% (wb). Determine the time (hr) required to dry the grain and the gallons of propane gas used assuming exit air is at 40% relative humidity.