<image>The process reflected by the function graph shown in the figure is: Xiaoming goes from home to the bookstore to read for a while, then goes to the school to pick up a letter, and immediately returns home. Here, $$x$$ represents time (unit: hours) and $$y$$ represents the distance Xiaoming is from home (unit: kilometers). The average speed of Xiaoming from the school back home is ______ kilometers/hour.
