Let volume of wooden block`=V`
volume of liquid displaced `=(4)/(5)N`
Weight of the block `=Vxx0.8xx10^(3)g`
As the block floats,
weight of the body `=` weight of the liquid displaced
`Vxx0.8xx10^(3)g=(4V)/(5)xxrho_(1)xxg, :. rho_(l)=10^(3)kg//m^(3)`