input: Write a function to count the number of occurrences of an element `x` in a list `y`. If the list is empty, return 0. 
  
  assert count_x(2, [3, 5, 2, 7, 4, 3, 2]) == 2
  assert count_x(3, [1, 2, 3, 3, 4]) == 2
  assert count_x(7, [1, 2, 3, 4, 5]) == 0
  assert count_x(0, []) == 0
output: def count_x(x, y):
      return y.count(x)