A 5,100 ft3 air stream exits a heating unit at 80°F and 60% RH and then mixes with 28,000 ft3 of air at 70°F and 40% RH provided to the building from another source. What is the combined dry-bulb temperature of the air in the building? Note: there is no exhaust in this problem. The total air quantity will be 28,000 ft3 + 5,100 ft3