input: Write a python function to filter even numbers from a list and return them.
  assert filter_even_numbers([3, 7, 10, 15, 17, 20])==[10, 20]
  assert filter_even_numbers([1, 4, 6, 9, 12])==[4, 6, 12]
  assert filter_even_numbers([2, 3, 5, 7, 8])==[2, 8]
output: def filter_even_numbers(lst):
      return [num for num in lst if num % 2 == 0]