It is given in the question that
M is the MIDPOINT OF FG.
[tex]FG = 26 \ AND \ GM = (3X - 2)[/tex]
Since M is the midpoint of FG, therefore GM is half of FG. That is
[tex]3X-2 = \frac{1}{2} (26)[/tex]
[tex]3X-2 =13 \\ 3X = 15 \\ X =5[/tex]
Therefore
[tex]GM = 3(5) -2 = 13[/tex]
And FM is 13 too .