First-Order Equations · Challenge problem

The equation $y'=2\sqrt{y}$ has many solutions with $y(0)=0$, because the equilibrium $y=0$ can be left at any moment. Suppose $y\ge0$ is differentiable on $[0,5]$, satisfies $y'=2\sqrt y$, $y(0)=0$ and $y(5)=9$. What is the largest $x$ in $[0,5]$ with $y(x)=0$?