Explanation:
Volume of water = volume of container = 12 cm * 18cm * 9 cm
so, volume of water = 1944 cm³ (since its filled full the container)
By the question in cubical container,
or, 1/3 of l³ = 1944 (formula for volume of cube is l³)
or, l³/3 = 1944
or, l³ = 5832
so, l = 18 cm
Length of each edge of cubical container is 18 cm.