The river is moving at 5 miles per hour. The river is 500 meters wide. A person can swim 15 miles per hour. Calculate the time it takes for the person to swim across to a point on the bank exactly opposite to his starting position and then back. Then calculate the time it takes for a person to swim upstream for 500 meters and then downstream for 500 meters back to his original starting position. Are these two times the same? Note: To end up at a point on the other side of the river exactly opposite to where he started, the person swimming across the river cannot aim himself at that point. The river will carry him downstream by a certain distance, depending on the speed of the river and the speed at which he swims.