input: Write a python function to find the median of a list of numbers.
  assert find_median([1, 3, 3, 6, 7, 8, 9]) == 6
  assert find_median([1, 2, 3, 4, 5, 6, 8, 9]) == 4.5
  assert find_median([2, 2, 4, 4, 5, 5, 7, 8, 9]) == 5
output: def find_median(numbers):
      numbers.sort()
      n = len(numbers)
      mid = n // 2
      if n % 2 == 0:
          return (numbers[mid - 1] + numbers[mid]) / 2
      else:
          return numbers[mid]