The document contains solutions to 3 chemistry problems: 1) A 50g rock sample with 80ppm copper contains 4 mg of copper. 2) A 2g seawater sample with 850ng silicon has a silicon concentration of 1.7 ppm. 3) With the ocean's average salinity of 35 ppt and mass of 1.4x1021 kg, it contains 4.9x1020 kg of salt.