Okay, lets solve for h
First off lets flip the equation \frac{1}{9g} +\frac{1}{9h} +\frac{-1}{9k} =f
Now add (-1)/9g to both sides
\frac{1}{9g} +\frac{1}{9h} +\frac{1}{9k} +\frac{-1}{9g} =f+\frac{-1}{9g}
\frac{1}{9h} +=\frac{-1}{9k} =f+\frac{-1}{9g}
Now add \frac{1}{9k} to both sides.
\frac{1}{9h} +\frac{-1}{9k} +\frac{-1}{9k} =f+\frac{-1}{9g} \frac{1}{9k}
\frac{1}{9h} =f+\frac{-1}{9g} +\frac{1}{9k}
Last you divide both sides by \frac{1}{9}
1/9h/1/9=f+-1/9g+1/9k/1/9
h=9f-9+k
Answer: h=9f-g+k
