input: def mean_median(arr):
      """
      Calculate the mean and median of a given array of numbers.
      >>> mean, median = mean_median([10, 15, 20, 25, 30, 35])
      >>> print("Mean =", mean)
      Mean = 22.5
      >>> print("Median =", median)
      Median = 22.5
      """
      arr_sum = 0 
      for i in range(len(arr)): 
          arr_sum += arr[i] 
      
      mean = arr_sum / len(arr) 
      
      arr = sorted(arr) 
      if len(arr) % 2 != 0: 
          median = arr[len(arr) // 2] 
      else: 
          median = (arr[len(arr) // 2] + arr[len(arr) // 2 - 1]) / 2
      
      return mean, median
output:     arr_sum = 0 
      for i in range(len(arr)): 
          arr_sum += arr[i] 
      
      mean = arr_sum / len(arr) 
      
      arr = sorted(arr) 
      if len(arr) % 2 != 0: 
          median = arr[len(arr) // 2] 
      else: 
          median = (arr[len(arr) // 2] + arr[len(arr) // 2 - 1]) / 2
      
      return mean, median