Four girls decided to use the same teeter-totter. Two of them weighing 75 pounds and 50 pounds, respectively, sat on opposite ends of the 12-foot board which had the balance point at the center. The third girl weighting 60 pounds got on the same side as the one weighing 50 pounds and sat 5 feet from the fulcrum. Where must the fourth girl sit so the teeter-totter is balanced if she weighs 40 pounds?