The gradient of a velocity-time graph is the acceleration.The sum of the positive values of the areas enclosed by the graph and the axes is the distance travelled.|area| = distanceSincearea = displacementareas under the x axis are displacement in the opposite direction so can be considered as negative displacements.If you add positive and negative displacements you will get the final displacement from the origin. If you add the positive values of the displacements you get the total distance travelled. If the areas under and above the x axis are equal the displacement will be zero.