The graph shows the vertical displacement y, in centimeters, that a weight bouncing from a spring would achieve if there were no friction, for a given number of seconds, x.
How is the weight moving during the time period x = 4 to x = 5?
From the graph we can observe that from x = 4 to x = 5, the graph just reached maximum before x = 4, it started moving towards 0, it crossed the zero line and started to move towards the minimum point.
In terms of the spring, this movement will be as: The weight reached its maximum height(extreme position) in forward direction just before x = 4 and then it started moving towards it mean position or the rest position. When it touches the x-axis, it is exactly at its mean position. Due to inertia (and no friction) the weight does not stop at its mean position and continues to move backward towards its other extreme position. At x= 5 the weight is just about to reach its extreme position.
