input: Write a python function to find the frequency of an element in a list.
  assert find_frequency([1, 2, 3, 4, 1, 2, 1], 1) == 3
  assert find_frequency([1, 2, 3, 4, 1, 2, 1], 2) == 2
  assert find_frequency([1, 2, 3, 4, 1, 2, 1], 3) == 1
  assert find_frequency([1, 2, 3, 4, 1, 2, 1], 5) == 0
output: def find_frequency(lst, element):
      return lst.count(element)