To find the dimensions of the tank, you will use the volume of a rectangular prism formula.
V = BH, where B is the area of the base and H is the height.
400 in^2 x 12 in
V = 4800 in^3
This volume would be less than 5000 cubic inches, so to find the dimensions, you will need to find 2 factors that equal 400 (20 in x 20 in).
All the dimensions would be length 20 in, width, 20 in, and height 12 in.