What is the density of the rock

The scale reads 3 so it is displacing 5 kg of water

find volume of rock using volume of water it displaces:

volume of rock = 5 kg (m^3 / 1000 kg) =.005 m^3

mass of rock = 8 kg

density = 8 / 0.005 (kg/m^3)

1600 Kg / m^3

You would have to find the mass and volume of the rock and then do mass divided by volume to get your density