Replace the words "a fraction" and "that fraction" with F

Replace the words "one quarter of F" with F

Replace the words "If I tripled" with "3×"

Replace the words "and multiplied it by" by "×"

Replace the words ", i would get" with an equal sign "=":

Replace the words "one twelfth" with 

We simplify that by changing 3× to  
and F×F to F²

 F² = 

We clear the fractions by multiplying both sides by 12.

 9F² = 1

We divide both sides by 9

  F² = 
   F = 

Either  or 

Edwin