# Finding an unknown point

I have this model: http://i.stack.imgur.com/rVfpU.jpg

What values do I have:

1) $D_M$

2) $D_L - D_R$

What I can't figure out, is how to calculate the $C$ position represented on this image.

I don't have $D_L$ and $D_R$ individually, just the difference of them.

If you could help with some reference on how I can calculate the $C$ position, I would be grateful.

You can't determine $C$ just from the difference. There's an entire one-dimensional curve of points that have the same difference of distances; in fact, this is one of the definitions of a hyperbola.