Fiberglass tub is old and stained with a crack near the drain
You can get tub and tile paint kits - I think rustoleum has one. Everything you need is in there.
Rustoleum or Homax tub and tile paint kits. Fill the crack with Bondo, auto body filler.
You can purchase the kits at home improvement stores. They include everything you need and instructions to use them. Hope this helps.