Exact Equations & Substitutions · Hard problem

The equation $(2 x y - 3)\,dx + (x^{2} + 6 y)\,dy = 0$ is exact. Its solution through $(-1, -2)$ is $\psi(x, y) = C$ for a potential $\psi$ with $\psi(0, 0) = 0$. Find $C$.