input: 
  def linear_search(arr: List[int], x: int) -> int:
      """ This function performs a linear search on the list 'arr' to find the first occurrence of 'x'. 
      If 'x' is found, it returns the index of 'x' in the list; otherwise, it returns -1. 
      Optimized to use Python's enumerate() function instead of manually iterating with range().
      
      Example:
      >>> linear_search([10, 20, 80, 30, 60, 50, 110, 100, 130, 170], 110)
      6
      >>> linear_search([10, 20, 80, 30, 60, 50, 110, 100, 130, 170], 200)
      -1
      """
      for index, item in enumerate(arr):
          if item == x:
              return index
      return -1
  
output:     for index, item in enumerate(arr):
          if item == x:
              return index
      return -1