This one is very confusing please help.

H was (Hx,Hy) goes to (Hy,-Hx)

G was (Gx,Gy) goes to (Gy,-Gx)

I was (Ix,Iy) goes to (Iy,-Ix)

Step-by-step explanation:

Rotating about the (0,0), the distance from any point to the origin (the hypotenuse of the triangle formed) never changes. A 90 clockwise rotation moves the point to the next quadrant, so side a and side b must flip to maintain the distance. You just need to flip the coordinates and change the sign of the new Y. If you plot a few random points and use a compass to rotate them 90 I think you will find this works.