A small fish tank is 40cm long, 20 cm wide and 20 cm high and its filled with water three quarters up its height.

Calculate the volume

Volume of the whole tank would be 20cm x 20cm x 40cm = 16 000 cm^3

3/4 of that is water

you can calculate how much of this volume is filled with water by creating a percentage factor

3:4 = 0,75 (75% of the tank is filled with water)

16 000 cm^3 x 0,75 = 12 000 cm^3

whole tank: 16 000 cm^3

water: 12 000 cm^3

check if you need to change the cubic centimeter to a different unit of volume

16,000 is if it's filled all the way

12,000 is filled up to 3/4

I think these are the answers. I'm so sorry if they are wrong.