I am assuming you need to find the volume since you need to find the amount of water. In real life the amount of water would be more than the volume of the ice. But as an estimate we can use volume.
To find the volume you multiply the 3 dimensions- length, width and height. 20 times 20 is 400. 400 times 20 is 8000 mm. So about 8000 mm water was needed.
Hope this helps! Brainliest Appreciated
