input: Write a python function to find the sum of even numbers in a list.
  assert find_sum([1, 2, 3, 4, 5, 6, 7, 8, 9]) == 20
  assert find_sum([10, 20, 30, 40]) == 100
  assert find_sum([1, 3, 5, 7, 9]) == 0
output: def find_sum(lst):
      return sum(num for num in lst if num % 2 == 0)