If the gradient of $f$ is $\nabla f = y^{2}\,\mathit{\vec j}-2z\,\mathit{\vec i}-3xy\,\mathit{\vec k}$ and the point $P = (-6, 5, -2)$ lies on the level surface $f(x, y, z)=0$, find an equation for the tangent plane to the surface at the point $P$.

$z=$