Official ExplanationIf s is the side length of a cube, then the cube’s volume = \(s^3\). Here, \(64 = s^3,\) so \(s = 4,\). Then AB = 4, and MA = NB = 2 in the figure below, because M and N are midpoints of two of the edges.

Now draw MB and form the two right triangles, MAB and MBN.

MB is the hypotenuse of a right triangle with legs equal to 2 and 4, so

by the Pythagorean Theorem. This length becomes a leg in the second right triangle MBN.

Therefore,
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