Because the density of water is 1g/mL and the density of ice is 0.9g/mL, water freezes and the quality of ice water remains unchanged, that is, the quality of water = the quality of ice.

Volume = mass/density

Let the mass of water be m.

Therefore, the volume of water before freezing is =m/ 1=m, and the volume after freezing is = m/0.9 = (10/9) m.

Then subtract the volume of water from the volume of ice and divide the difference by the volume of water.

Just push the ice water back.

I haven't worked out the result, you can do it yourself.