If we have a cube, we know that the cube has 6 sides of equal length.
The volume of a cube is Volume = S x S x S = (S)^3, where S is one of the six side lengths.
Here we know that the long expression is the Volume of the cube.
If we take the third root of that expression, meaning find an expression that when taken to the power of 3 gives us that long expression, we find 4x - 5, because (4x - 5)^3 = 64x^3-240x^2+300x-125 = S^3
Since we are looking for the side length of the cube and we know that Volume = S^3 (S is the side length) and that the Volume of this cube is Volume = (4x - 5)^3
Then we can say that S^3 = (4x - 5)^3, which is the Volume. To get the value of just S, because that's what we are trying to find, we take the third root of both sides to get:
S = 4x - 5 --> Therefore, the side length of the cube is 4x - 5.
@saa15