speed relative to

While walking between gates at an airport, you notice a child running along a moving walkway. Estimating that the child runs at a constant speed of 2.7 m/s relative to the surface of the walkway, you decide to try to determine the speed of the walkway itself. You watch the child run on the entire 22-m walkway in one direction, immediately turn around, and run back to his starting point. The entire trip takes a total elapsed time of 32 s. Given this information, what is the speed of the moving walkway relative to the airport terminal?