The weight of block in air will be density times the volume of block(0.08 X 7840 = 627.2kg) and the subtracting the density of water times the volume of block(0.08 X 1000 = 80kg) from this we'll get the weight of block in water (627.2 - 80 = 547.2kg). Now we have to find the answer in Newtons so simply multiply it with 9.8 (547.2 X 9.8 = 5,362.56N).