To find the length of the side of the 64 units ² square , simply take the root of the area,

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To find the length of the side of the 64 units ³ cube , simply make an equation,

Calculate the product and then take the root of both sides and get, x = 4
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Now, we subtract since " difference " means to subtract...
8 - 4 = 4
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Answer : 4
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I hope that helps you out!!
Any more questions, please feel free to ask me and I will gladly help you out!!
~Zoey