input: def mean_median(arr):
      """
      Read an array from the user and then determine the mean and median of the array.
      
      Example:
      >>> 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)