Question 956938

Let's switch coordinates and look at G using M as (0,0).
From M to G, the x distance is {{{5-(-8)=13}}}
and the y distance is {{{-9-3=-12}}}
So in M coordinates, G is (13,-12).
To rotate about M by 90 degrees then G becomes (12,13) or (-12,-13) depending on positive or negative rotation by 90, since you didn't specify.
Remember these are in M coordinates.
So to change back to the original coordinates, we have to add back the coordinates of M.
(12,13)+(-8,3)=(4,16)
(-12,-13)+(-8,3)=(-20,-10)
So now if we reflect about {{{y=9}}}, you find the y-distance from {{{y=9}}} and then add that distance to 9 to get the new y-coordinate.
So for (4,16), the distance from {{{y=9}}} is {{{16-9=7}}}.
Since the point is above {{{y=9}}}, we will subtract 7 from the {{{y=9}}} to get the reflected point.
(4,9-7)=(4,2)
and for (-20,-10), the distance to {{{y=9}}} is {{{9-(-10)=19}}} so then add 19 to {{{y=9}}} 
(-20,9+19)=(-20,28)
So then G' is either (4,2) or (-20,28).