The equation defines $y$ is a function of $x$.
Work Step by Step
For an equation to be a function, it must satisfy the following requirement: Every value of $x$ must correspond to exactly one value of $y$. In this case it is true, because if we plug in any number in the place of $x$ the value of $y$ will be clear. For example, for $x=2$, $x^3=2^3=8$, therefore $y$ can only have $8$ as a value if $x=2$.