Halliday, Resnick & Walker — Waves–I: Problem Problem_55

The following two waves are sent in opposite directions on a horizontal string so as to create a standing wave in a vertical plane: \[ y_1(x, t) = (6.00 \text{ mm}) \sin(4.00\pi x - 400\pi t) \] \[ y_2(x, t) = (6.00 \text{ mm}) \sin(4.00\pi x + 400\pi t) \], with \( x \) in meters and \( t \) in seconds. An antinode is located at point \( A \). In the time interval that point takes to move from maximum upward displacement to maximum downward displacement, how far does each wave move along the string?