The volume of a rectangular prism = width x height x length so just plug 6 x 3.5 x 1.25 into a calculator and you'll get the answer
Finding the volume of a cube involves multiplying with this formula.
Height * Width * Length = volume
To find what the side lengths are, we can take the cube root of 64.
∛64 = 4
Height = 4
Width = 4
Length = 4
These sides are multiplied together to get 64.
The only answer choice that makes sense is Option A.
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