input: Write a function to count occurrences of a given element in a list.
  assert count_x(1, [1, 2, 3, 1, 1, 4]) == 3
  assert count_x('a', ['a', 'b', 'a', 'c', 'a', 'd']) == 3
  assert count_x(0, [0, 0, 0, 0, 1, 2, 3]) == 4
output: def count_x(x, lst):
      return lst.count(x)