A runner is jogging in a straight line at a steady vr= 7.7 km/hr. When the runner is L= 2.1 km from the finish line, a bird begins flying straight from the runner to the finish line at vb= 30.8 km/hr (4 times as fast as the runner). When the bird reaches the finish line, it turns around and flies directly back to the runner.
runner's remaining time: 2.1/7.7 = 0.27 hours
during that time, the bird flies 8.4 km