The volume of a rectangular prism is the product of its 3 dimensions: length, width and height.
Then, the product of the three dimensions has to be equal to 60 cubic inches for the 3 prisms.
All the units are in inches, so we don't have to do any conversion.
Rectangular Prism A

The length of A is 6 inches.
Rectangular Prism B

The width of B is 3 inches.
Rectangular Prism C

The height of C is 3 inches.