input: Write a function to perform a linear search on a list.
  assert linearSearch([1, 2, 3, 4, 5], 3) == 2
  assert linearSearch([10, 20, 30, 40, 50], 25) == -1
  assert linearSearch([7, 8, 9, 10, 11], 11) == 4
output: def linearSearch(lst, target):
      for i in range(len(lst)):
          if lst[i] == target:
              return i
      return -1