What is the value of $x$ if a cube's volume is $5x$ cubic units and its surface area is $x$ square units?
So the volume is $s^3$, where $s$ is the side length of the cube. So the surface area is $6s^2$. The problem gives us two equations: $s^3 = 5x$ and $6s^2 = x$. We can use the second equation to substitute for $x$ in the first equation. Plugging in $x = 6s^2$, we get $s^3 = 5(6s^2)$. Simplifying, we get $s^3 = 30s^2$. To solve for $s$, we can divide both sides by $s^2$, as long as $s \neq 0$. This gives us $s = 30$. Now that we have $s$, we can use either equation to find $x$. Using the second equation, we get $x = 6s^2 = 6(30)^2 = 5400$. So the value of $x$ is 5400. 