input: 
  from typing import List
  from math import floor
  
  
  def mean_median(arr: List[float]) -> (float, float):
      """Given an array of numbers, calculate and return the mean and median.
      >>> mean_median([10, 15, 20, 25, 30, 35])
      (22.5, 22.5)
      """
  
output:     arr.sort()
      n = len(arr)
      mean = sum(arr) / n
      if n % 2 == 0:
          median = (arr[n//2 - 1] + arr[n//2]) / 2
      else:
          median = arr[n//2]
      return mean, median