1. Take the dimensions of the aquariums and multiply them to get the cubic inches,
2. Take the known time and divide the cubic inches of the aquarium that was filled.
3. Take the result from step 2 and multiply it by the cubic inches of the other aquarium. That will be the time that it will take to fill the other aquarium.
cubic inches = the product of the dimensions
time to fill a cubic inch = time divided by cubic inches
time needed to fill aquarium = time to fill a cubic inch times cubic inches.