input: Write a python function to fix a string by removing spaces, converting to lowercase, and reversing the string.
  assert fix_string("Hello World") == "dlrowolleh"
  assert fix_string(" Python ") == "nohtyp"
  assert fix_string("OpenAI") == "ianepo"
  assert fix_string(" 123 ") == "321"
output: def fix_string(s):
      return s.replace(" ", "").lower()[::-1]