In the picture, we have two triangles. Since EDG was bisected, that means angle EDF and angle FDG are equal. We also see that the triangles contain 90 degree angles as well. Since two of three angles are the same, this means the third angle must also be the same. Because the triangles contain the same angle measurements, they are similar. Because they both share the same side, and all three angles, then the two triangles must be congruent.
This means that EF = FG
or, equivalently
n + 9 = 4n - 6
Solve this equation for n, then plug that value into FG
