Answer:
side length= 4 mm
Explanation:
The explanation is pretty easy;
You know that to get the volume of a cube the formula is length times width times height. You also know that all sides of a cube are equal. so what multiplied by itself 3 times = 64?
That would be 4; 4 times 4 = 16 then 16 times 4 = 64
Sorry if the explanation wasn't great:(