Answer:
The dimensions of a rectangular prism are 21 in. by 20 in. by 19 in.
To find:
The volume of the rectangular prism.
Solution:
Let the length, breadth and height are 21 in, 20 in and 19 in respectively.
Volume of the rectangular prism is



Therefore, the volume of the rectangular prism is 7980 cubic inches.
If the question is how many shelves are needed, then the answer is 18 shelves.
6 * 3 = 18 + 2 = 20
improper fraction will be 20/3