A cubical wooden box floating on water rises 1cm when 400 gm of stone is

removed from it. What will be volume of this box?

I'm not sure you can do this without just a bit more information. I can tell you what the mass of the water is when the rocks are removed. When we know that, we know the volume of the water that was displaced. whether or not this is enough information to determine the volume of the box, I'm not sure.

400 grams raises the box 1 cm.

The density of water = 1 gm / cm^3

400 grams of water = 400 mL or 400 cm^3

The volume of the displaced water = 400 cm^3

The volume a slice from the square prism is B*h

B = 400 cm^2

h = 1 cm

If the base is 400 cm^2 then each side is

s^2 = 400

sqrt (s^2) = sqrt (400)

s = 20

The volume of the box is 20^3 = 8000 cm^3