Image distance of light in parallel mirrors question

[salmayoussef]

Homework Statement

[/B]
Two parallel mirrors that face each other are placed along and perpendicular to the x-axis at x = +7.40 m and x = -7.40 m. Assume that a point source of light is placed on the axis at x = +3.30 m. In principle, there will be an infinite number of images generated. Consider the locations of the four images of the point source with the smallest absolute values of image distance i.

Going from left to right (i.e from negative to positive), what is the x-coordinate of the left most image?
I drew the x-axis looking sort of like this:

--------|-----------|-----|-------|-------- x
-7.4 0 3.3 7.4

I tried 18.1, but that didn't work, then I tried x=10.7 (7.4+3.3) but that didn't work either.
Any help would be greatly appreciated!

Edit: a better diagram http://m.imgur.com/leGcHvs

 

[haruspex]

Your 'better diagram' is unviewable.
Let the mirrors be at +y and -y. Consider an image at position x. Where will the two reflections of that image appear?
Once you have those two formulas, you can apply them in turn to generate a list of images.