You have that A = (9,2), B = (4,-4)
In order to find the coordinates of C, a point at the middle of the segment AC, you calculate the midpoint of each couple of coordinates.
For the first coordinate:
[tex]\frac{9+4}{2}=\frac{13}{2}=6.5[/tex]For the second coordinate:
[tex]\frac{2-4}{2}=\frac{-2}{2}=-1[/tex]Hence, the coordinate of C is C = (6.5 , -1)
For the case of the points (4a,5g) and (-6a,-g), you have:
[tex]\begin{gathered} \frac{4a-6a}{2}=\frac{-2a}{2}=-a \\ \frac{5g-g}{2}=\frac{4g}{2}=2g \end{gathered}[/tex]Hence, the midpoint is (-a,2g)
[tex]\frac{5g-g}{2}=\frac{4g}{2}=2g[/tex]