Answer
$y=\sqrt x-2$
Work Step by Step
We need to find the anti-derivative for $\dfrac{dy}{dx}=\dfrac{1}{2\sqrt x}$
Thus, we have: $y=x^{1/2}+C$
Apply the initial condition $y(4)=0$ in the above equation to solve for $C$.
we get: $2+C=0 \implies C=-2$
Hence, $y=x^{1/2}-2$ or, $y=\sqrt x-2$