The correct option is deposition. Deposition is the process by which sediments, soils and rocks are added to a particular rock which result in successive layers in the rock. Deposition is usually brought about by the action of wind, water, ice and gravity. These forces brings on sediments which are added to the rock layers.
You find this by taking the total distance of the first lap and doubling it. You could also find it by adding 400 meters to 400 meters, which would total at 800 meters