I need help in understanding how to do these problems: 1. Tracy leaves for work at 8 A.M. traveling at 36 mph. Sarah finds that Tracy has forgotten her briefcase, so she leaves at 8:05 chasing after her at 50mph. At what time will Sarah catch Tracy? 2. Two jets leave St. Louis at 2 P.M., one traveling north at 850km/h and the other south at 750km/h. At what time will they be 4000km apart? 3. It takes a train 90min longer to go from Fartmington to Allentown at 60km/h than it does to return at 80km/h. What is the distance between these towns? These are the "rate x time = distance" problems. How do I figure out what goes where?