input: Write a python function to check if a number is a multiple of 3.
  assert check_multiple_of_3(9)=="Number is multiple of 3"
  assert check_multiple_of_3(10)=="Number is not a multiple of 3"
  assert check_multiple_of_3(15)=="Number is multiple of 3"
output: def check_multiple_of_3(n):
      if n % 3 == 0:
          return "Number is multiple of 3"
      else:
          return "Number is not a multiple of 3"