<image>A truck travels from location A to location B at a constant speed, unloads the cargo in half an hour upon arrival at B, and then returns at a constant speed. It is known that the truck's speed on its return trip is 1.5 times the speed it had when traveling from A to B. The graph of the function $$y($$ kilometers$$)$$, which represents the distance of the truck from A as a function of time $$x($$ hours$$)$, is shown in the figure. Hence, $$a=$$_ _ _ _ __$$($$hours$$)$$. 