Two children are walking at the same steady speed of 5 feet/second at the United terminal at O'Hare airport. One steps on the moving walkway and continues walking, while the other continues along the regular floor. The moving walkway moves in the direction of the child's motion with speed 5 feet/second. The first child stops at the end of the moving walkway and waits 4 seconds for the second child to catch up. How long is the moving walkway (in feet)? Provide a numerical answer without units.
