Can someone help me with this problem? I do not know how to work it...
x = 9 (the square root of x)
The reason you missed the x = 0 solution is that you divided both sides by $\displaystyle \sqrt{x}$ which is an invalid procedure when x = 0.
Tip: When you are dividing both sides of an equation always remember to set that factor equal to 0 to see if there might be another solution in there.
-Dan