Plexiglass
Well Dennis, it is easier to replace scratched plexiglass than to repair. However, if it can't be replaced and labor is cheap, I have successfully repaired scratches in aircraft windshields. Wag Aero at 1-800-558-6868 sells a Micro-Mesh kit for $21.50. The kit consists of a series of unique sandpaper sheets plus other things. What you do is slowly sand out the scratches by using finer and finer sandpaper. However, ordinary sandpaper will not work so don't try it