Answer: The height and width of the aquarium are 13 inches and 10 inches respectively .
Explanation:
Given : The volume of aquarium = 2730 cubic inches
Length of aquarium = 21 inches
Let x be the width of the aquarium,
then Height = x+3
We consider the shape of aquarium as cuboid.
Volume of Cuboid = Length x width x Height
Put values in the above formula , we get

So , the width of aquarium =x= 10 inches ( width cannot be negative)
So height = 10+3=13 inches.
Hence, the height and width of the aquarium are 13 inches and 10 inches respectively .