Weight of cork in air = 5g. Upthrust on cork = (Weight of cork in air + Weight of sinker in water) - (Combined weight in water) = (5 + 86) - 71 = 20g. Since upthrust = volume * density_water, Volume of cork = 20 cm³. Density of cork = mass/volume = 5g / 20 cm³ = 0.25 g/cm³ = 250 kg/m³.