input: Write a function to perform a linear search and return the index of the item if found, otherwise return -1.
  assert linear_search([1, 2, 3, 4, 5], 3) == 2
  assert linear_search([10, 20, 30, 40, 50], 60) == -1
  assert linear_search(['apple', 'banana', 'cherry'], 'banana') == 1
  assert linear_search(['a', 'b', 'c', 'd', 'e'], 'e') == 4
output: def linear_search(lst, item):
      for index, element in enumerate(lst):
          if element == item:
              return index
      return -1