A certain cube has volume n cubic inches and surface area n square inches. What is the value of n?
Let's denote the side length of the cube as $s$ inches. The volume of the cube is equal to $s^3$ cubic inches, and the surface area is equal to $6s^2$ square inches.
We are given that the volume is equal to the surface area, so we have $s^3=6s^2$. Dividing both sides by $s^2$ (note that $s$ cannot be 0), we have $s=6$.
Therefore, the value of $n$ is equal to the volume and surface area, which is $s^3=6^3=\boxed{216}$.