3d Geometry

If the plane 2x – y + 2z + 3 = 0 has the distances $${1 \over 3}$$ and $${2 \over 3}$$ units from the planes 4x – 2y + 4z + $$\lambda$$ = 0 and 2x – y + 2z + $$\mu$$ = 0, respectively, then the maximum value of $$\lambda$$ + $$\mu$$ is equal to :