a. One thousand tones (1000 t, 1 t = 10³kg) of sand contains about a trillion (10¹²) grains of sand. How many tones of sand are needed to provide 1 mol of grains of sand?

b. Assuming the volume of a grain of sand is 1 mm3and the total land area of the United States is 3.7 × 10⁶ mi², how deep would the sand pile over the United States be if this area were evenly covered with 1 mol of grains of sand? (1 mi = 1 mile = 1.609 km)