The feasible region is bounded, and $z = 4x + 6y$ is the objective function. Compute $z$ at the corner points: \[ z(0, 2) = 12, \quad z(3, 0) = 12. \] Since $z$ has the same value at $(0, 2)$ and $(3, 0)$, any point on the line segment joining these points also gives the minimum value of $z$.