Physicists/Math Gurus - Need your brain power.?

I am creating a puzzle based upon Newton's Law of Universal Gravitation (F= G((m1 x m2)/r squared) I am trying to work backwards so that F gives me two pre-selected numbers: 4328804 and 11201129. If we assume the mass of the two objects are 45.3592kg and 56.600kg respectively (converted 100lbs and 125lbs to kg) I get the result of 2571.8212808. So that should be decided by the distance between them squared. The result should be multiplied by G to get my desired results. But for the life of me, I can't work it backwards to find the value of the distance needed to get each desired result (I seem to come close, but off). I have been using an on-line scientific calculator so maybe the limitations there is screwing me up. Just as an FYI - I am making a puzzle and the results should be North and West coordinates. (geocaching thing). Thanks for your help.....I'll post the link to the puzzle when I am done and thank you in it (your user name unless you tell me different). Newton's Formula: http://csep10.phys.utk.edu/astr161/lect/history/gr...