Kelly sank down into a seat at the back of the subway car, glad for the chance to rest a bit after a hectic day. Derrick, her 2-year-old son, squirmed on her lap as the ride began. He soon settled...

Kelly sank down into a seat at the back of the subway car, glad for the chance to rest a bit after a hectic day. Derrick, her 2-year-old son, squirmed on her lap as the ride began. He soon settled down, however, apparently fascinated with their surroundings, and before long she was dozing. Mistake! Suddenly the child leaped from her lap and charged down the aisle, giggling at the trick he’d played on his mom. By the time Kelly was fully awake and had started running after him, he was 6 yards ahead of her. Relative to the track outside, Derrick was moving at 33 mph, and Kelly was moving at 35 mph (the train’s speed was 30 mph). How long did it take her to catch Derrick? How far from her seat were they when she caught him?