A marathon runner runs at a steady 15

km/hr. When the runner is 7.5 km from the finish, a bird begins flying from the runner to the finish at 30 km/hr. When the bird reaches the finish line, it turns around and flies back to the runner, and then turns around again, repeating the back-and-forth trips until the runner reaches the finish line. How many kilometers does the bird travel?

BLUE: 10 km PINK: 20 km

PURPLE: 15 km GREEN 30 km