determine the flow of the vector field $\textbf{A}=|r|^{-3}\textbf{r}$ out of the cube defined as -L<x<L , -L<y<L , -L<z<L where $\textbf{r}=(x,y,z)$

Question

I want to determine the flow of the vector field $\textbf{A}=|r|^{-3}\textbf{r}$ out of the cube defined as -L<x<L , -L<y<L , -L<z<L where $\textbf{r}=(x,y,z)$

Should I just think of the cube as 6 surfaces and calculate the flow out of each surface by using parametrisation, or is there an easier way to do it? (since this method would give me 6 separate integrals). I also don't understand why the flow is not zero since we are integrating something that is asymmetrical over something that is symmetrical. Any help is appreciated!