edge length is 40 inches.
The edge length of a cube has the same measurement.
Volume of a cube is computed by multiplying the edge length to itself twice.
Volume = edge length x edge length x edge length
If the given data is volume of the cube and edge length is required. simply find the cube root of the volume.
edge length = ∛volume
edge length = ∛64000 in³
edge length = 40 inches.
To check:
40 x 40 = 1600 x 40 = 64000