On a postition versus time graph to find the acceleration you would simply find the area under the graph right? and how would you figure out whether acceleration is increasing, decreasing, constant of unknown from a graph? My guess is that the accereration is constant throughout.
to find acceleration on a position time graph is hard. The slope of the position curve on p-t graph is velocity, and then on a v-t curve, the slope at any point is acceleration.
http://en.wikibooks.org/wiki/FHSST_Physics_Rectilinear_Motion:Graphs