Exact Equations & Substitutions · Hard problem

The equation $(6 x y - 2)\,dx + (3 x^{2} + 2 y)\,dy = 0$ is exact. Its solution through $(2, 3)$ is $\psi(x, y) = C$ for a potential $\psi$ with $\psi(0, 0) = 0$. Find $C$.