input: Write a function to combine two strings and reverse the result in Python. The function should take two strings as input and return the reversed combined string.
  assert combine_and_reverse("Hello ", "world!")=="!dlrow olleH"
  assert combine_and_reverse("Python ", "programming!")=="!gnimmargorp nohtyP"
  assert combine_and_reverse("OpenAI ", "is amazing!")=="!gnizama si IAepnO"
  assert combine_and_reverse("Task ", "completed!")=="!detelpmoc ksaT"
  assert combine_and_reverse("", "")==""
output: def combine_and_reverse(str1, str2):
      return (str1 + str2)[::-1]