An auto mobile accelerates at4mls 2 to the power from 20 mls to 36m/s How long did that acceleration take

Use the profile illustrated for problem (1). assume that the layer of silty sand fill (sm) is placed over the entire site. estimate the thickness of the fill (h - in feet) that will cause the effective vertical stress at the center of the clay layer to increase by 517.5 pounds per square foot.