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Subj:.....Sarah's Age (S274b, S529c) 
          From: LABLaughs.com on 2/19/2002
Drawing from DeviantArt.net...
Source: http://www.afunzone.com/adailypuzzle/12-10-08.html

Sarah's new teacher asked her, her age.  She replied: 
"My age today is three times what it will be three 
years from now minus three times what my age was three 
years ago."  How old is Sarah? 

Finger pointing down
from darrell94590 on 1/2/2006
Drawing from Ripleys-Believe It Or Not

                  THE SOLUTION

Sarah is 18.

If she is 18 then three times her age three years from
now would be 21x3 (63).
Three times her age three years ago would be 15x3 (45).
Subtract 45 from 63 and she is 18.

The equation is S = 3(S+3) - 3(S-3).