Consider the following. (a) Sand dunes on a desert island move as sand is swept up the windward side to settle in the leeward side. Such \"walking\" dunes have been known to travel 21 feet in a year and can travel as much as 85 feet per year in particularly windy times. Calculate the average speed in each case in m/s. 21 ft/y = 1 m/s 85 ft/y = 2 m/s (b) Fingernails grow at the rate of drifting continents, about 10 mm/yr. Approximately how long did it take for North America to separate from Europe, a distance of about 3000 mi? Solution Sorry, but I do not understand the problem. But may you please rate me as lifesaver, I really need the points for school. Thank you very much..