How to Determine the Image Charges for a Dielectric Interface?

[BREAD]

Homework Statement

What collection of image charges solves the problem in above pictured ??

Homework Equations

The Attempt at a Solution

One of the image charge should be in dielectric region
q'=-((e2-e1)/(e2+e1))

 

[Dr Transport]

What book has this problem, it is a good one...this one will take some time to figure out.

 

[Dr Transport]

I see 7 image charges in this one and they are not trivial to calculate...