A rock weighs 143 g in air and 82 grams in H2O, What is m of H2O displace? Volume H2O displaced?

61g for the m of H20 is correct. Water is 1 gram per mL, so your volume of water displaced is 61 mL. This also means that the volume of the rock is 61 cm^3 (a milliliter and a cubic centimeter are the same thing). Density is m/volume, so the density is 143g/61cm^3. Your units for density are g/cm^3.